Question 1

What is the maximum cable length for a Modbus RTU network?

Accepted Answer

We recommend that the total cable length per segment does not exceed 1.000 m. (Total cable length = sum of the main network line and all branches).    Modbus RTU should follow a line topology, so avoid making branches on the main line. If branches are present, they should be kept as short as possible. The combined length of all branches should not exceed 20 m.    When the total cable length becomes too high, the Modbus RTU communication will be disturbed. To compensate these communication losses due to cable length, a Modbus repeater (e.g. DPOM-24-20) can be used to compensate cable length.

Question 2

What cable to use for a Modbus RTU network?

Accepted Answer

Sentera advises to use Shielded Twisted Pair (STP) or Unshielded Twisted Pair (UTP) cable to connect Sentera devices via Modbus RTU.    The wires should have the following characteristics: - Characteristic impedance: 120 Ω ±10% - Specific resistance depending on network length    Modbus RTU has a line topology - the Modbus RTU should be connected from device to device and branches should be minimised.

Question 3

What power supply to use for my PoM network?

Accepted Answer

Sentera devices can be connected together via ‘PoM’ or ‘Power over Modbus’. This means that both Modbus RTU communication and 24 VDC power supply are distributed via one Unshielded Twisted Pair (UTP) network cable.    Larger networks containing many devices, should be split into different segments. For each segment, the total current consumption must remain limited to 1,5 A maximum.    To select the correct power supply, calculate the total sum of the maximum current consumption of all connected devices in the segment. Select a power supply with sufficient capacity to provide power supply to all connected devices, based on this sum. We advise to use not more than 90 % (*) of the maximum capacity of the power supply to compensate power losses in the cables and inrush currents during start up.    (*) Depending on the products connected to the PoM network.

Question 4

What does ‘IP protection’ mean?

Accepted Answer

IP rating, sometimes referred toas International Protection rating, or Ingress Protection rating classifies the degree of protection provided by the drive enclosure against both solid objectsand liquids. The IP code, defined by International standard IEC 60529, generally consists of two digits that classify the level of protection providedin each case.    Sentera products are available in enclosures with different IP ratings, dependent of the model range andspecifications required. Consult the product datasheets for further information on available ranges. A summary of the available IP ratings for Sentera productsare given below.    IP20 Enclosures provide someprotection from accidental contact from hands / fingers and no protection against the ingress of dust, water or other liquids into the product’s enclosure.These devices are designed to be installed in an electrical cabinet with sufficient ventilation and cooling possibilities.    IP30 Enclosures provide protectionagainst contact from hands / fingers and smaller objects (e.g. screwdriver). They don’t offer protection against the ingress of dust, water or other liquids into the product’s enclosure. These devices are designed for indoorapplications.    P54 Enclosures protect againstingress of dust to the point of preventing ingress of anything potentiallyharmful to the internal workings of the device. On top of that, the enclosure also withstands water splashing from different directions (no water jets). These devices are designed for applications in harsher environments or outside if protected against rain and direct sunlight with a cover.    IP65 Enclosure is rated ascompletely dust tight and protected against exposure to water jets from anydirection. These devices are designed for outdoor applications.    The level of IP protection you will require is dependent on your application and the conditions the Sentera device will be exposed to, and by any local regulations that are applicable to your application. Generally, if unsure, then always seek advice and elect to go with the higher IP rating.

Question 5

What motor insulation class is required in combination with a fan speed controller or VFD?

Accepted Answer

The insulation of the motor windings prevents short circuits in the windings or connection of the winding to the protective earth. The class of insulation of a motor winding defines the strength of insulation required with respect to maximum temperature rise of the motor. Different motor types have different temperature rise characteristics in function of the duty cycle and the size of the motor enclosure. Usually Class F insulation (or higher) is suitable for VFD use.

Question 6

What is the difference between a transmitter, intelligent sensor and sensor controller?

Accepted Answer

Sentera offers devices to measure or control following parameters: temperature, relative humidity, CO2, air quality (TVOC), CO, NO2, ambient light, differential pressure, volume flow and air velocity.    A transmitter or sensor is a device that measures a certain parameter. The device translates this measured value into an analogue output (0-10 VDC / 0-20 mA / PWM) or Modbus RTU register.    An intelligent sensor has the possibility to define different ranges for different parameters. These types of sensors only have one single output. When all measured values are at their minimum range, the sensor output will remain at its minimum value. When one of the measured values approaches the maximum range, the sensor output will also increase towards its maximum. This functionality makes it possible to control air flow in function of different parameters with a simple, intelligent sensor. The parameter with the narrowest range has the highest influence on the sensor output.    A sensor controller offers the possibility to define a setpoint (via Modbus RTU). By controlling its output, the sensor controller will try to keep the measured values as close as possible to the setpoint values.    Click here to discover our range of HVAC sensors.

Question 7

What is the difference between an AC induction and synchronous AC motor?

Accepted Answer

In both induction and synchronous motors, the AC power supplied to the motor stator windings create a magnetic field that rotates in time with the AC oscillations.    The rotor of a synchronous motor is equipped with permanent magnets. A PMSM (Permanent Magnet Synchronous Motor) uses permanent magnets embedded in the steel rotor to create a constant magnetic field. The stator carries windings produce a rotating magnetic field. At synchronous speed the rotor poles lock to the rotating magnetic field. These motors are not self-starting and therefore they need to be combined with a frequency inverter to be able to operate them.  The magnetic field in the rotor of an induction motor is created solely by induction instead of being self-magnetized as in permanent magnet motors. For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stators rotating magnetic field; otherwise the magnetic field would not be moving in relation to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors.    For induction motors, following international efficiency standards have been defined: IE1, IE2, IE3, IE4 and IE5. Synchronous motors are often referred to as PMSM (Permanent Magnet Synchronous Motors), BLDC (Brushless DC) motors or SyncRM (Synchronous Reluctance Motors). All these types of motors can be controlled via our frequency inverters.    - Understanding fan speed control

Question 8

How to regulate fan speed with AC synchronous motors?

Accepted Answer

A Sentera frequency inverter or Variable Speed Drive (VSD) allows you to control the speed of AC synchronous motors. Frequency inverters generate an almost perfect sinusoidal motor voltage via Pulse Width Modulating (PWM) technology using IGBTs (Insulated Gate Bipolar Transistors). The ratio of voltage to frequency is kept constant, resulting in an optimal motor control and very silent operation of both motor and frequency inverter.   Available for single or three phase motors up to 46 A.    The desired motor speed can be adjusted manually via a knob (local or remote control) or in function of CO2, air quality or another parameter (demand based). In this second scenario, an HVAC sensor is connected to the fan speed controller to calculate the optimal fan speed. More information can be found on the Sentera solutions page.    - Understanding fan speed control

Question 9

How to regulate fan speed with EC motors?

Accepted Answer

An EC motor or Electronically Commutated motor can be seen as an AC motor with integrated fan speed controller.    This means that an EC motor requires an indication of the desired fan speed or a fan speed setpoint. The most common ways to provide this information to the EC motor are: - Potentiometer that sends a 0-10 VDC (analogue) signal to the EC motor (*) - HVAC sensor that sends a 0-10 VDC (analogue) signal to the EC motor (*) - HVAC sensor that sends the desired fan speed via Modbus RTU to the EC motor (**) - HVAC controller that sends the desired fan speed via Modbus RTU to the EC motor (**)    (*) Some Sentera devices can also generate a 0-20 mA or PWM signal. (**) In this case, an EC motor with Modbus RTU communication is required. The motor type should be compliant with Sentera PoM devices.    - Understanding fan speed control

Question 10

How to send the desired fan speed to my EC motor or my AC fan speed controller?

Accepted Answer

The best way to do this is via Modbus RTU. The advantages of this recent, digital technology is the immunity for interferences. Thanks to this technology, you will be able to use longer cables – up to 1.000 m - without the risk of losing information. Devices that are connected via Modbus RTU can exchange a lot of information – not only the desired fan speed – and it is also possible to monitor and control them via internet.    The older - analogue - technology is still present in many installations. In these installations, the desired fan speed is usually transmitted via 0-10 VDC / 0-20 mA or PWM. The disadvantage of this technology is the sensitivity for interferences. If cable lengths are > 10 m, the maximum value received at the other side of the cable will not be 10 VDC anymore due to cable resistance. Also power cables nearby the signal cable, EMC pollution or magnetic fields can disturb the analogue signal. And since only the desired fan speed is transmitted, there is no possibility to monitor the status of the connected device or other parameters via internet.    More information can be found on the Sentera solutions page.    - Understanding fan speed control

Question 11

Can I control multiple motors with one fan speed controller?

Accepted Answer

Yes, that is possible.    If doing so, make sure that: - All connected motors are identical. - The fan speed controller is selected, based on the total motor current required, by adding together the rated current of all the connected motors. The selected fan speed controller must have a maximum current rating that is equal or higher than this sum. - Each motor is protected by an individual thermal overload. - The motors remain permanently connected to the fan speed controller and are not individually started or stopped whilst the fan speed controller is enabled. - When using a frequency inverter: operate in V/F Mode only and apply an output filter.  In the scenario of one fan speed controller per motor, each motor can be controlled separately and run at a different speed. This is not the case when multiple motors are controlled via one fan speed controller. Secondly, running multiple motors from one fan speed controller creates a single point of failure.

Question 12

Kick start versus Soft start - what is the difference?

Accepted Answer

Kick start and soft start are two different ways to start up a motor or fan. The best acceleration method depends on your application. Applications with high inertia might need a higher torque at start up to avoid stalling of the motor.    Kick start — the motor will accelerate immediately from standstill towards maximum speed. The full motor torque is almost immediately available. After this start-up period (typically 8 – 10 s), the motor will decelerate towards the requested fan speed setpoint. This starting method is often used to avoid motor stalling at low speed. The disadvantage is the mechanical stress at start-up and a high motor start current.    Soft start — the motor will smoothly accelerate from standstill towards the requested fan speed setpoint. This starting method gives you the advantage of reduced mechanical stress and lower motor starting currents. Due to the reduced motor torque during start up, this acceleration method is not ideal for high inertia applications.

Question 13

What is a PWM signal?

Accepted Answer

PWM or “Pulse Width Modulation” (also known as “Pulse Duration Modulation” or PDM), is a modulating control signal, comparable to an analogue 0-10 VDC or 0-20 mA signal. It can be used to send the requested rotational speed to an EC motor or AC fan speed controller. Another application example is to transmit the requested position to an actuator powered damper.    Typically, the EC fan speed will increase in proportion to the value of the analogue 0-10 VDC or 0-20 mA signal. For a PWM signal – a continuous train of electronic pulses consisting of a HIGH and LOW part - this works as follows: - The frequency of the PWM signal determines the duration of one complete HIGH / LOW cycle. For example, a frequency of 1.000 Hz means: every second, the PWM signal counts 1.000 HIGH / LOW cycles. - The comparison of the duration of the HIGH part, compared to the FULL signal (expressed in percent and also called “duty cycle”) determines the speed at which the motor or fan should run or in case of an actuator powered damper, the requested position.  A power supply is required to generate a PWM control signal. Most Sentera devices with analogue output feature an integrated power supply (3,3 VDC or 12 VDC), but in case the EC motor requires a PWM signal with a specific amplitude, an external power source should be applied.    So when using a Sentera device to control a fan (or actuator powered damper) via PWM, make sure that both the frequency (in Hz) and the amplitude (in VDC) of the modulating output of the Sentera device correspond to the frequency and amplitude requested by the external device.

Question 14

Can a Sentera device with Modbus RTU communication work stand alone?

Accepted Answer

Yes.   All Sentera devices with Modbus RTU communication can be used standalone or they can be integrated in a Modbus RTU network. In many situations, the default parameter settings will be enough to start using the product. For the applications where some parameters need to be adjusted or optimised, we advise you to use Sentera’s free 3S Modbus software. Connect the Sentera device to your computer and the 3S Modbus software will automatically recognise the connected device. The Modbus input registers are read-only, the holding registers can be modified.

Question 15

How to adjust parameters of a Sentera device?

Accepted Answer

All parameters of Sentera devices can be read and adjusted via Modbus RTU communication. These parameters can be subdivided into Input registers and Holding registers. Input registers are read-only. They contain information that can be read, but they cannot be modified. The values of the Holding registers can be changed. Settings that determine the functionality of the device are usually contained in Holding registers. For a complete overview of all parameters, consult the Modbus register map of the device.   To  facilitate configuration and monitoring of your Sentera device, we advise to use one of  following options:    3SM software This software allows you to monitor or configure Sentera devices. Install the 3SModbus software and connect your Sentera device(s) to the computer. We advise to use the CNVT-USB-RS485-V2 converter to connect your Sentera device(s) to the computer. The connected devices are automatically detected. By clicking on them, you can monitor or change the parameter settings.    - 3SMcenter - Sentera configuration software                                                                  ' alt='video' src='C:\BEA\Temp\Jos\3SModbus_configuration_software_How_to_configure_Sentera_products.png'>     Sensistant configurator If you do not want to use a computer to configure your Sentera device, SENSISTANT is the best option. SENSISTANT is a Modbus configurator. Connect SENSISTANT to a Sentera HVAC sensor or fan speed controller and adjust the settings.    - SENSISTANT - Sentera product configuration tool                                                                    ' alt='video' src='C:\BEA\Temp\Jos\How_to_configure_Sentera_transmitters_and_fan_speed_controllers.png'>     SenteraWeb Via a Sentera internet gateway, you can connect Sentera device(s) to SenteraWeb. Via SenteraWeb, it is possible to configure and to monitor parameters. Also data logging is possible.

Question 16

What is the difference between an AC and EC motor?

Accepted Answer

A motor which is referred to as ‘AC motor’ has a stator winding. The AC power supplied to the motor stator creates a magnetic field that rotates in time with the AC oscillations. This magnetic field is used to generate the motor torque. AC motors (and certainly induction motors) are relatively cheap and have a simple construction, compared to DC motors. At the other hand, DC motors offer a very high energy efficiency.  Brushless DC motors are also known as EC motors (or Electronically Commutated motors). They are synchronous DC motors, powered by a DC electric source via an integrated fan speed controller which produces an AC electric signal to drive the motor. The integrated controller uses a DC current switched on and off at high frequency for voltage modulation and passes it through three or more non-adjacent windings. Because the controller must direct the rotor rotation, the controller requires some means of determining the rotors orientation/position (relative to the stator coils). Some designs use Hall effect sensors or a rotary encoder to directly measure the rotors position.    An EC motor can be seen as an AC motor with integrated fan speed controller. This means that an EC motor requires an indication of the desired fan speed or a fan speed setpoint. Many EC motors can be controlled via an analogue 0-10 VDC or PWM signal. More and more EC motors feature Modbus RTU communication. The advantage is that they cannot only be controlled via Modbus RTU, but all the motor parameters (Rpm, consumed power, motor status, motor temperature, etc.) are also available via Modbus RTU.    - Understanding fan speed control

Question 17

What is ‘PI control’?

Accepted Answer

What is PI-Control?   PI Control is a feedback control loop mechanism that calculates a correction by taking the difference between the desired set point and the measured value. Common applications are cruise control, temperature control, etc.    The controllers PI algorithm restores the measured value to the desired set point with a minimal delay and   overshoot.   - The P stands for proportional and represents the size of the calculated correction. The closer the measured value is to the set point, the smaller the corrections must be.   - The I stands for Integral and looks at how the difference between set point and measured value evolves in time when applying the correction.    Both P & I are parameters that can be set manually in the PI-controller. When activated (and available), the auto-tune function of the PI Controller calculates the optimal P- and I-parameters based on the real-time response of the process to different control values.

Question 18

How to regulate fan speed with AC induction motors?

Accepted Answer

An AC voltage controllable motor is an AC induction motor that can be controlled by varying the motor voltage. Sentera offers different types of fan speed controllers for these types of motors, based on different technologies:    Technologies that regulate the motor speed by reducing the motor voltage: - Transformer fan speed controllers feature a 5-step speed control for AC voltage controllable motors. These fan speed controllers with autotransformers provide a simple, yet robust solution to control the fan speed by adjusting the voltage of the AC voltage controllable motor in steps. In some cases, the fan speed controller can produce a humming noise due to the autotransformer technology, but the motor will be very quiet. Available for single or three phase voltage controllable motors up to 20 A. - Electronic fan speed controllers feature an infinitely variable speed control for AC voltage controllable motors. These fan speed controllers use Phase angle control (TRIAC technology) to adjust the motor voltage and to control the fan speed. Thanks to this technology, the fan speed controller will be very quiet. Depending on the motor type, the motor can cause a humming noise at lower speeds. Available for single or three phase voltage controllable motors up to 10 A. - AC choppers feature an infinitely variable speed control for single phase AC voltage controllable motors. These fan speed controllers adjust the motor voltage via PWM (Pulse Width Modulating) technology using IGBTs (Insulated Gate Bipolar Transistors). Compared to Electronic fan speed controllers, AC choppers generate an almost perfect sinusoidal motor voltage. Both motor and fan speed controller will be very silent. Available for single phase AC motors up to 2,5 A.    For those AC induction motors that cannot be controlled by varying the motor voltage, a frequency inverter or Variable Speed Drive (VSD) is required.    Frequency inverters generate an almost perfect sinusoidal motor voltage via PWM (Pulse Width Modulating) technology using IGBTs (Insulated Gate Bipolar Transistors). The ratio of voltage to frequency is kept constant, resulting in an optimal motor control and very silent operation of both motor and frequency inverter. Available for single or three phase motors up to 46 A.    In all of these scenarios, the desired motor speed can be adjusted manually via a knob (local or remote control) or in function of CO2, air quality or another parameter (demand based). In this second scenario, an HVAC sensor is connected to the fan speed controller to calculate the optimal fan speed. More information can be found on the Sentera solutions page.    - Understanding fan speed control

Question 19

What is indoor air quality or IAQ?

Accepted Answer

In the developed world, we spend 90% of our time indoors. Research shows that key pollutants are up to five times more concentrated inside than outside. According to WHO, around 3.8 million people a year die from the exposure to household air pollution. This indoor air pollution comes from a variety of sources, and includes a wide range of gases, chemicals and other substances.    When we make our homes more airtight, we risk to that VOC levels will start to build up. VOCs or Volatile organic compounds in indoor environments evaporate from substances such as cleaning products, adhesives, paints, new carpets, copiers and printers to building materials and furnishings. VOCs are also emitted from humans and animals in their breath, sweat and directly from their skin. VOCs are known to cause eye, nose and throat irritations, headache, drowsiness, dizziness, nausea, difficulty concentrating and fatigue.  Closing doors and windows keeps the heat inside, but it also leads to a more humid environment, especially as we dry clothes on radiators or tumble dryers, rather than outdoors. Higher humidity causes mould, moisture and condensation, which all impact our health negatively.    It is our mission to optimise your comfort, indoor air quality and to contribute to your health in a positive way and therefore, Sentera developed a complete range of HVAC transmitters – the eyes of a smart ventilation system – to monitor and optimise your indoor air quality. Based on these measurements, the fan speed can be optimised to improve indoor air quality and realise energy savings.    What’s in it for you?   Well, these are the short-term benefits of a good indoor air quality: - Better breathing - Better sleep - Elimination of allergens - Reduced odours - Balanced humidity - Reduced energy costs    - Measure and monitor air quality

Question 20

Why to measure temperature and relative humidity?

Accepted Answer

Temperature and relative humidity have a direct impact on the sense of well-being and comfort of the residents.    Dry air leads to dry skin, itchy eyes, and irritated nasal passages. It can cause a bloody nose or an itchy throat and can aggravate symptoms of the common cold and some respiratory ailments. It also increases static electricity, which you feel in your clothes and hair and on furniture and carpeting.    Too high relative humidity degrees will result in condensation forming on windows, walls and ceilings that are colder than the air temperature and potentially damaging building materials and causing odours in poorly ventilated spaces. Condensation describes when a gas condenses back into a liquid and is more often used when referring to water vapour condensing back into liquid water. Water condensation usually happens when water vapour cools and appears as droplets on a surface or appears as clouds or water droplets in the sky. The condensation process will facilitate the growth of moulds and bacteria that can cause respiratory problems and/or allergic reactions. It provides the conditions for dust mite populations to grow, which can affect asthma sufferers.    Relative humidity The ratio of water vapour in the air to the maximum amount of water vapour the air can hold at a particular temperature is expressed as relative humidity (rH). For example, rH of 30% means that the air contains 30% of the moisture it can possibly hold at that particular temperature. When air can hold no more moisture at a given temperature (i.e. the rH is 100%), the air is said to be saturated.    Dew point temperature The dew point is the temperature to which air must be cooled to become saturated with water vapour. When further cooled, the airborne water vapour will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface. The measurement of the dew point is related to humidity. A higher dew point means there will be more moisture in the air.    Since temperature and relative humidity are basic parameters that determine the comfort and well-being of residents, most Sentera sensors can measure these.    Ventilation in function of temperature and relative humidity level is interesting in rooms where large fluctuations in temperature or relative humidity regularly occur, such as kitchen or bathroom.    - Measure and monitor air quality

Question 21

Why to measure CO2?

Accepted Answer

CO2 - NDIR CO2 sensing technology Carbon Dioxide or CO2 is not only a by-product of combustion, it is also the result of the metabolic process in living organisms. Because carbon dioxide is also a result of human metabolism, concentrations within a building are often used to indicate whether adequate fresh air needs to be supplied to the space. Ventilation systems that are controlled based on the measured CO2 level can control the fresh air supply depending on the occupants and their activity level.  Moderate to high levels of carbon dioxide can cause headaches and fatigue, and higher concentrations can produce nausea, dizziness, and vomiting. Loss of consciousness can occur at extremely high concentrations. To prevent or reduce high concentrations of carbon dioxide in a building or room, fresh air should be supplied to the room.    NDIR is an industry term for “nondispersive infrared”, and is the most common type of sensor used to measure CO2. CO2 gas molecules absorb the specific band of IR light while letting other wavelengths of light pass through. Finally, an IR detector reads the amount of light that was not absorbed by the CO2 molecules or the optical filter. The difference between the amount of light radiated by the IR lamp and the amount of IR light received by the detector is measured. The difference is proportional to the number of CO2 molecules in the air inside the room.    Ventilation based on CO2-level is interesting in rooms with highly variable occupancy, such as meeting rooms, classrooms, universities, etc.    - Measure and monitor air quality

Question 22

Why to measure TVOC or indoor air quality?

Accepted Answer

VOC - Volatile Organic Compounds Volatile Organic Compounds or VOCs are organic chemicals that become a gas at room temperature and are the main origin of air pollution at ground level. A common term used when measuring and eliminating VOCs is “Total VOC” or TVOC. TVOC means the total concentration of multiple VOCs present simultaneously in the air.    The human contribution to indoor air pollutants has been historically correlated with CO2, which is commonly used as an indicator for insufficient ventilation in closed spaces, but this doesn’t cover the complete load.   VOCs or Volatile organic compounds are known to cause eye, nose and throat irritations, headache, drowsiness, dizziness, nausea, difficulty concentrating and fatigue. VOCs in indoor environments evaporate from substances such as cleaning products, adhesives, paints, new carpets, copiers and printers to building materials and furnishings. VOCs are also emitted from humans and animals in their breath, sweat and directly from their skin.    Among many VOCs, TVOC sensors have an increased selectivity to hydrogen (H2). In indoor environments, the H2 concentration is expected to correlate well with the CO2 concentrations as human breath contains significant concentrations of both CO2 (4 %) and H2 (10 ppm). Furthermore, humans are the major source of CO2 and H2 in typical indoor environments. This makes it possible to distinguish the influence of human presence from other contaminants and  control the ventilation system based on occupation of a space.    Ventilation in function of TVOC level is interesting in environments where indoor air quality need to be optimised on continuous base, such as living room, office buildings, certain industrial environments, etc.    - Measure and monitor air quality

Question 23

Why to measure CO and NO2?

Accepted Answer

Shopping malls, office buildings, large hotels, event venues … Car parks are increasingly important in large building projects. The enclosed atmosphere in an underground car park makes us wonder: how do we keep garages clear from car exhaust fumes?    When cars with combustion engines move around an enclosed parking garage, they release toxic gases like nitrogen dioxides (NO2) and carbon monoxide (CO). Due to the typically low ceiling, underground and enclosed car parks present a particular challenge to ventilation systems. Such a smart ventilation system must prevent the accumulation of toxic from motor exhaust and therefore, it needs a sensor adapted to these conditions.    Sentera designed a special range of sensors for these applications. These devices measure temperature, relative humidity, carbon monoxide (CO) and nitrogen dioxide (NO2) levels as well as ambient light and are available in different enclosure types.

Question 24

What is Modbus RTU?

Accepted Answer

Sentera devices exchange information via a network, called Modbus RTU.    Modbus RTU is a serial communication protocol that uses RS485 technology. In simple terms, it is a method used for transmitting information over serial lines (RS485) between electronic devices. The device requesting the information is called the Master and the devices supplying information are slave devices. On a standard Modbus RTU network, there is one Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can also write information to the Slaves.

Question 25

What is PoM or Power over Modbus?

Accepted Answer

Sentera products share information via Modbus RTU communication. Modbus RTU is a serial communication protocol that uses RS485 technology.    The term ‘PoM’ stands for ‘Power over Modbus’. It refers to a technology that both Modbus RTU communication and the 24 VDC power supply for the connected devices are distributed via one single UTP cable (Unshielded Twisted Pair cable). This makes it possible to connect different HVAC sensors via one cable. By using 3-way splitters, it is possible to create short branches to connect a device to the main line.    Some Sentera sensors have classic terminal blocks. In this case a UTP cable with loose wire ends is required. Sentera -M series HVAC sensors can be connected via one simple RJ45 connector. Sentera 24 VDC power supplies are also available with RJ45 connectors. This makes it possible to interconnect all Sentera devices with UTP cables with RJ45 connectors. This makes wiring more efficient and reduces the risk of wrong connections.    This movie shows how easy it is to crimp an RJ45 connector:    ' alt='video' src='C:\BEA\Temp\Jos\How_to_crimp_an_RJ45_connector_for_a_Sentera_PoM_network.png'>

Question 26

What is an electronic fan speed controller for AC motors?

Accepted Answer

How to control AC fan speed in an easy way? Electronic fan speed controllers make it possible to adjust the rotational speed of AC fans. These variable speed drives are very easy to install and to configure.    The Sentera product range features variable speed drives for single or three phase AC voltage controllable motors and fans in HVAC applications. Electronic variable fan speed controllers allow you to regulate the speed of AC fans manually or demand based. Phase angle control (TRIAC technology) is used to adjust the motor voltage and to control the fan speed. Thanks to this technology, these speed controllers are completely silent. Depending on the motor type, some additional motor noise at low speed might occur. Fan speed controllers offer you advantages in terms of comfort - optimisation of the supply of fresh air in your building, in terms of health - improvement of the indoor air quality as well as in environmental terms - thanks to the optimised airflow, your ventilation system will be more energy efficient.    - Understanding fan speed control

Question 27

Can I use a Sentera transmitter for agriculture or horticulture applications?

Accepted Answer

Some of  Senteras duct and outdoor CO2 transmitters are optimised for agriculture and horticulture applications. The measuring ranges are adjusted to the needs of the agricultural and horticultural industry and the electronics are treated with a special coating, making them extra corrosion resistant. CO2 concentrations up to 10.000 ppm can be measured. For more details, search for: DSMH or ODMH.

Question 28

How to control 3-speed fans?

Accepted Answer

A 3-step control switch can be used to adjust the speed of single phase 3-speed fans. Sentera 3-step control switches are available with or without OFF position. They connect the 230 VAC mains to either the start winding of the motor or to one of the connection points on the main winding of the motor. So, the 230 VAC is connected to only one of the three contacts. This allows you to adjust the fan speed from low to high in 3 steps.

Question 29

What is a potentiometer?

Accepted Answer

A potentiometer is a device to generate a control signal. Typical control signals are: 0-10 VDC, 0-20 mA or 0-100 % PWM. These infinitely variable control signals or analogue signals can be used to control an EC fan, a frequency inverter, a variable speed drive, a damper actuator, etc. In simple words, this means that they can be used to manually adjust fan speed or damper positions. Some potentiometers require a supply voltage, while other types are unpowered - these types dont need a supply voltage.

Question 30

What is a control switch for EC fans?

Accepted Answer

While a potentiometer generates an infinitely variable control signal, a control switch generates a stepped control signal. The 0-10 V analogue signal is divided in 3 or 4 steps. This allows you to manually adjust fan speed or damper positions in 3 or 4 steps.

Question 31

How to use a ventilation system during COVID-19?

Accepted Answer

The risk of transmission of the SARS-CoV-2 virus via aerosols appears to be rather low outdoor or in enclosed spaces with a large volume. In addition to the usual standard hygiene measures, REHVA – the Federation of European HVAC associations - advises to increase ventilation in order to reduce the risk of contamination or transmission via the air. They advise to deactivate indoor air recirculation, to increase the supply rate of fresh air and the extraction rate of stale air. The ventilation system should be activated on continuous base. For non-occupied spaces, the air volume flow can be reduced to save energy.    In case no ventilation system is available, they advise active operation of window airing in combination with the monitoring of indoor air quality. Sentera advises to use CO2 transmitters or air quality sensors to monitor your indoor air quality. These HVAC sensors are designed to monitor indoor air quality. Long before occupants will perceive bad air quality or lack of ventilation, Sentera HVAC sensors will alert you to open the window.    - Measure and monitor air quality

Question 32

What is the difference between 3-wire and 4-wire connection?

Accepted Answer

Sentera -F and -H sensors require a supply voltage of 24 VDC. This type of sensors require a 4-wire connection. They can be connected with a 4-wire electrical cable: 2 wires for the supply voltage and 2 wires for the output signal. The ground connection of the supply voltage and the analogue output are galvanically separated in -F type sensors. That is why they require a 4-wire connection.    4-wire connection reduces the risk of electrical interferences since the supply voltage and the output signal remain completely separated.    Sentera -G sensors require a supply voltage of 24 VAC or 24 VDC. This type of sensors require a 3-wire connection. They can be connected with a 3-wire electrical cable. The ground connection of the supply voltage (V-) is internally connected with the ground of the analogue output (GND). It is called a common ground. This means that only 3 wires are required to connect the supply voltage and the analogue output. Due to this common ground, -G and -F type sensors cannot be used together on the same network.    Never connect the common ground of -G type sensors to other devices powered by a DC voltage. Doing so might cause permanent damage to the connected devices.

Question 33

How does an NDIR CO2 Sensor Work?

Accepted Answer

NDIR is an industry term for 'nondispersive infrared', and is the most common type of sensor used to measure carbon dioxide or CO2 in HVAC applications.    A non-dispersive infrared (NDIR) sensor has a detector that measures how much infrared light of a specific wavelength is absorbed by the surrounding air. This measurement is then used to calculate the CO2 concentration. Major advantages of NDIR sensors are the low life-cycle cost and a precise and stable long-term operation.    Sentera CO2 sensors use the ABC Logic self-calibration algorithm. Thanks to this algorithm, the drift in the NDIR sensors is automatically corrected in normal indoor applications. This eliminates the need to manually recalibrate the sensors. This results in a maintenance-free sensor with an with an exceptionally long life expectancy.    - Sentera CO2 sensors

Question 34

How to recalibrate a CO2 sensor?

Accepted Answer

Sentera CO2 sensors do not require manual recalibration. They use an intelligent calibration algorithm to automatically recalibrate themselves once they are installed. This feature eliminates one of the biggest concerns surrounding CO2 sensing: sensor drift and routine maintenance for recalibration.    Virtually all gas sensors are subject to some sort of drift, including CO2 sensors. The degree of drift is partially dependent on the use of quality components and good design. But even with good components and excellent design, a small amount of drift can still occur in the CO2 sensor. This may ultimately result in the need for a sensor to be recalibrated. Such manual recalibration process is simple but it is time consuming and therefore it can turn into a significant expense if recalibration is required frequently. Thanks to the intelligent recalibration algorithm, the sensor service life is extended and significant (maintenance) cost savings can be realised.     How does the automatic recalibration algorithm work? The microprocessor of the sensor remembers the lowest CO2 concentration that occurred during the past 24 hours. This low point is assumed to be the outside CO2 level. The sensor is smart enough to discount periodic elevated readings that might occur if, for example, a space was exceptionally used 24 hour per day. Once the sensor has collected 14 minimum CO2 levels, it performs a statistical self-analysis. If the analysis concludes that there is sensor drift, a small correction factor is made to the sensor calibration to compensate the drift.    It is important to notice that Sentera CO2 sensors are designed for applications where spaces are periodically unoccupied for 4 hours per day or more so that indoor CO2 concentrations can drop down to typical outside levels.    If a Sentera CO2 sensor is applied in an application that is unlikely to see regular outdoor CO2 concentrations, then the self-calibration algorithm should be deactivated. This can be done via Modbus Holding Register 40. By default, the self-calibration algorithm is enabled.

Question 35

How to restore the factory default settings of a Sentera device?

Accepted Answer

The settings of Sentera products can be changed via the parameters in the Modbus Holding registers. We distinguish between communication parameters and operational parameters.    Resetting the communication parameters is hardware-based. Such a reset is often required when communication via software is no longer possible. To reset the Modbus communication parameters to their factory default values, put a jumper on pins 1 and 2 of the P1 header for at least 5 seconds.    The operational parameters can be reset via the 3SModbus configuration software or via the Sensistant Modbus configurator by activating Holding register 10. By doing so, all operational parameters are reset to their factory default value. It is also possible to manually reset individual parameters to their factory default value via the software.    This video shows how the hardware and software reset are performed on an HVAC sensor:    ' alt='video' src='C:\BEA\Temp\Yves\How_to_restore_the_factory_default_settings_of_a_Sentera_device.png'>

Question 36

What is Ecodesign regulation EU 2019/1781?

Accepted Answer

The European Union (EU) Ecodesign Directive is focused on making sure we get the maximum possible performance out of any energy that is consumed. The directive provides consistent EU-wide rules for improving the environmental performance of products, from household appliances to engineering products.    The EU has set targets for energy efficiency and CO2 emission to help limit the average global temperature increase to 1,5°C. To support this objective, the latest Ecodesign Regulation EU2019/1781 came into effect in October 2019 and now includes variable frequency drives (VFDs) along with a wider range of motors. A second phase, which expands the scope of the regulation and increases the requirements for motors, will commence on 1st July 2023.    The latest Ecodesign Directive introduces International Efficiency (IE) classes for variable frequency drives. From 1st July 2021, specified VFDs must meet IE2 specification. Our three-phase frequency inverters meet these requirements. Single-phase frequency inverters, electronic fan speed controllers and transformer fan speed controllers are not contained in this regulation.

Question 37

What does IE2 mean for VFDs?

Accepted Answer

The Ecodesign regulation EU 2019/1781 covers 3-phase standard drives with a diode rectifier in the range 0.12 kW ≤ Pn < 1000 kW. After 1st July 2021, the power losses of these drives shall not exceed the maximum power losses corresponding to the IE2 efficiency level. The International Efficiency level (IE) is given at the nominal point. After 1st July 2021, drives covered by the regulation must be IE2 compliant as a minimum in order to be CE marked.    Single-phase drives and fan speed controllers are excluded from this regulation.

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