Where NTC temperature sensors are used?
In daily life and industry, there are many types of sensors which are indispensable for many systems in our daily lives.
The most common types of such sensors are temperature sensors. This is a device (standalone or part of some device) that measures the ambient temperature and sends the data to the control point.
The ntc devices are some of the cheapest. Their simple operating model allows them to be used in many different formats and locations. So, for example, the ntc 10k temperature sensor is used on the arduino to make its own systems and boards. 10k can be connected to your device to monitor the desired temperature.
Main types of sensors
The main principle of all sensors. is the conversion of the signal and interpretation of the result to promptly inform the user about changes in the work of the gas boiler.
The gas appliances are equipped with a set of accessories, thanks to which they can be programmed to operate in a certain mode.
Key sensors responsible for the safety of the equipment:
Different types of thermistors, locations and how to remove them from a boiler
Consider the characteristics and features of operation of each of them.
To determine the strength of the draught in the appliance, the draught sensor or thermostat for the gas boiler is used, it is also responsible for the correct combustion of gas.
The draught is necessary to rid the boiler of carbon monoxide. Normal draught “takes out” combustion products from the room, but not in it, weak draught can cause fading of the boiler and as a consequence, an accident.
Most often these sensors are installed in a smoke trap. In case of sensor failure, the smoke from the products of combustion penetrates into the room and creates a threat to life safety.
The type of sensor depends on the type of boiler you want to connect it to. The first type. boilers with natural draught, the second. with forced.
In units with natural draught, the combustion chamber is open. During normal operation, carbon monoxide escapes through the chimney, and a safety thermostat monitors the draft and temperature of the exhaust gases. Such boilers use a sensor in the form of a metal plate with a contact attached to it.
The principle of its operation is to signal the valve, which at the right time will shut off the gas flow to the burner. There is a metal strip inside the thermostat which reacts to temperature changes.
The thermostat is set at a certain temperature according to the fuel in the boiler. If natural gas is used, the temperature range will be from 75 ° C to 950 ° C in the case of liquefied. 75-1500 ° C.
If there is a failure in the process of carbon monoxide escape (through the chimney to the street), in other words, if the draught is violated, the device activates. When this occurs, the temperature inside the boiler rises, the metal expands, the sensor activates and the boiler cools down.
Owners of gas appliances with natural draught should pay attention to the concept of “reverse draught. In simple terms, it is a process whereby carbon monoxide enters the room rather than being vented into the chimney.
Failure occurs with temperature fluctuations, improper installation of the chimney or its clogging, can also affect inaccurate calculations of the size of the chimney. Regardless of the cause of back draft, it must be eliminated immediately to prevent carbon monoxide poisoning.
Forced draft units have a closed combustion chamber and the gas is exhausted by a turbine-fan. A pneumatic sensor in the form of a diaphragm is used here.
During normal draught, the membrane is slightly deformed by the force of carbon monoxide. When the flow becomes too weak and the diaphragm is left without movement, the contacts disconnect and the gas valve closes. Such sensor controls both fan operation and speed of combustion products.
If there are doubts about the operation of the device that interrupts the gas supply in case of a leak, it is advisable to install a carbon monoxide sensor next to the gas equipment. Its installation is strongly recommended, but not obligatory.
Causes of activation of the draught sensor: errors in the installation of the boiler or chimney, chimney blockage or fan stoppage (only for units with forced draught).
The principle of operation and devices of the gas boiler automation system are described in detail in the following article, with which we
Pressostat operating principle
Pressostat or pressure sensor protects the boiler from overheating during sudden changes in gas pressure or reduction of water flow.
Visually. it is a standard electrical sensor or relay, in most cases with two electrical circuits-adjusters. It is these circuits that determine the two key modes of operation of the device:
- 1 operation mode assumes normal pressure, during which the thermostatic membrane of the sensor does not change location and the first contact group is closed. The boiler operates in normal mode by passing a current through this circuit. It is also always connected to the main circuit of the unit.
- 2nd mode is activated when any system parameter is out of norm. The thermostatic diaphragm inside the relay is displaced and deflected. The first controller circuit is disconnected, thanks to the diaphragm, and the second circuit is closed. Boiler equipment stops working correctly. Standby mode, which informs the user of the boiler of an alarm, is activated by the secondary circuit of the sensor.
The sensor triggers even in the case of the slightest increase in temperature in the combustion chamber. It monitors the minimum/maximum value of the pressure force and also registers the beginning of condensation in the combustion products or directly in the gas itself.
What the overtemperature sensor monitors?
The overheat sensor is a small device that protects the gas boiler from boiling, which can occur when the temperature rises above 100 °C. When the limit temperature in the heating circuit is reached, the overheating sensor disconnects the contacts and shuts down the gas appliance.
The basis of the device are either thermistors or biometric plates, sometimes it can be working NTC sensors.
Causes of overheating of the gas boiler and options for their elimination:
- Lack of circulation in the heating circuit due to clogged filters. All filters must be cleaned carefully, rinsed or replaced with new ones if necessary.
- “Air bleeding” of the heating circuit. To get rid of it, you can simply remove the air.
- The flow is clogged due to a large layer of scale, and you can hear as if the boiler “bangs” or makes popping noises. Remove the excess in the appliance with special chemicals or acids.
- Noises can be heard during the boiler start-up and the device may display an “insufficient circulation” error. This situation is possible when starting the boiler, after a long downtime and without first running the ventilation system. The cause can be a clog in the pump due to downtime. The pump must be disassembled and thoroughly flushed and then restarted.
- The place of installation of the equipment has been chosen incorrectly. In this case, if the room is high humidity or low temperature, the metal from which the boiler is made, will begin to deteriorate quickly.
At any cause of overheating it must be immediately removed to avoid damage to the boiler or an explosion. To get rid of overheating the user can both independently and using the services of an experienced master.
Outdoor and room temperature sensors
The main task of the temperature sensor for the gas boiler is to control the temperature and inform about its changes in time. Modern response devices work on the principle of electrical resistance, which allows you to record the operating readings.
According to the method of transmission of information temperature sensors are:
- wired (communicate with the controller by means of a cable);
- wireless (wireless radio communication is used for signal transmission, such models consist of 2 parts).
According to the type of control they are divided into simple (maintain the temperature in the room) and programmable (there are many functions to influence the thermal regime in the house).
Some models have a built-in thermostat that allows you to control the humidity level in the room. They also have a humidity decreasing/increasing function.
According to the method of placement, the following devices are distinguished:
- Overhead. mounted on heating pipes;
- immersed. are in constant contact with the coolant.
In this case, the indoor ones are located directly in the room, and outdoor are set outside and respond to temperature changes outside the window.
The first two types are used for the heating medium, t.е. for the boiler, and the other two. to control the air temperature. Surface-mounted are mounted on the outer surface of the pipeline with a special tape or clamp.
Immersion water heating sensors for the boiler are placed only in special places inside the unit in close proximity to the heating medium.
The response element for measuring the degree of temperature can be an electrical transducer (thermocouple, resistance thermometer), pre-set to a certain range. Such devices may be with a display, some models are provided in advance the possibility of calibration.
Outdoor temperature sensor allows the boiler to operate not all the time, but only as needed. This increases the life of the gas boiler and the consumption of gas itself. When installing it, you should consider protection from mechanical and weather (moisture, frost) effects in advance.
The set of remote equipment includes:
- the sensor itself;
- terminals for clamping the electric cable;
- cable coupling;
- plastic housing, which will house all the parts of the device.
When the temperature changes outside the window, the sensor of the gas boiler activates the weather program, which makes changes to the temperature mode of heating water heating.
Room sensor reacts to changes in temperature in the room, then sends information to the automation, which controls the boiler. And already it gives a signal to reduce or increase the heating power of the heating circuit.
The principle of operation is that the user must initially set the desired temperature in the room, and the equipment itself will control the gas equipment.
The boiler will only start if the ambient temperature in the room to be heated is lower than the temperature set before. Thus, you will reduce your monthly gas bill by about a third.
When selecting a temperature sensor, pay special attention to the temperature range. The optimal choice would be from 10 ° C to 70 ° C. Also consider the threshold temperature. There are models that react to a decrease in temperature by 1/4 degree.
This is not very convenient, because the boiler will often turn off. However, most are triggered when the temperature changes to 0.5 or 1 degree.
The dimensions of the device itself are mostly small: 23 cm. With wired models, the cable length should be at least 5 m. If wireless communication will be used, be sure to test the radio signal.
The rules and nuances of adjusting the gas heating equipment automatics are described in detail in the article, the material of which is fully devoted to this issue.
Flame detector. a reliable protection for your boiler
One of the key factors that guarantee safe operation of the gas boiler is a flame detector. Its main task is to send a signal about the attenuation of the flame on the burner as quickly as possible to the automation system to shut off the gas to prevent it from leaking and exploding the entire device. Also, this sensor should inform the controller about the quality of gas combustion, the presence of flame, and the intensity of combustion.
Types of flame detectors
They depend on the method of flame control during operation of the gas boiler. Control can be direct or indirect. Thermometric, photoelectric, ultrasonic, ionization and refer to the direct methods.
Indirect is considered to be the control of the formation of carbon monoxide in the furnace, the fuel pressure in the pipeline through which it comes, the force of the pressure or its fluctuations in front of the burner. This also includes checking for an inextinguishable ignition source.
Based on the thermoelectric method of monitoring, the sensor includes a thermocouple (sensor and solenoid valve are included). The thermocouple is placed in close proximity to the boiler burner, and the solenoid valve is mounted on the gas line that supplies gas to the ignited burner.
Many modern units are installed sensors of flame ionization. Their principle of operation is that when the flame burns between the body and the sensor electrode, an ionization current is generated. It is generated in the case of an attraction of ions. If there is no such current, it becomes a signal to stop the gas supply.
If the flame of the igniter produces the necessary amount of free electrons and negative ions, the automatics activates the key device that enables the main burner to operate.
Please note that the correct operation of the ionization sensor is only possible with a precise phase connection of the heating boiler to the power grid.
It is this mechanism is much more effective than others in the case of gas combustion, because gas does not actually produce light, so the photocell does not always react. Infrared persists for a little longer, which may be enough time for a large amount of gas to accumulate, which automatically makes the infrared flame detector less safe.
Photo sensors monitor the flame of the key burner, but they are not used to diagnose the flame of the igniter because of the insufficient size of its flame. Such sensors are divided by their reaction to the wavelength of light flux: some are triggered by the visible and infrared spectrum of light flux from a burning flame, while others “see” only its ultraviolet component.
For correct operation, photo sensors must have a “direct contact” with the burner flame, so they are mounted in close proximity to it. They are installed on the side of the burner at an angle of 20-30° to its axis. Because of this, photosensors are subject to overheating by heat radiation from the walls of the unit and heating through the inspection window.
In order to protect the photodetector from overheating, heat-resistant quartz glasses and forced blowing, which is carried out either by compressed air with reduced pressure or by fan air, are used.
Flame detector can be triggered. When the key gas-air ratio is disturbed or the igniter or the valve gets dirty. If the flame sensor is broken for any reason, it should be replaced immediately. It will save life and health of you and your family.
Equipping the gas heating equipment with a full set of safety sensors and automation devices does not eliminate the need for regular maintenance. How to carry out inspections and repairs on gas appliances is described in detail in our recommended article.
Replacing the Ntc Temperature Sensor for Gas Boilers
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uncle_diver
Let me start by saying that I have a gas boiler Viessmann Vitodens 100-W. This is a very good, economical and powerful condensing boiler. Requires no attention, no squeezing, no jumping. In general, Viessmann and Buderus. they are the top of the boiler industry. And those who choose them will never regret their choice. The problem is not only that boilers are expensive, but also that optional “hangings” for them cost a lot of money. I’m talking about the extra gauges. Firstly, it is an absolutely essential boiler sensor. Without it the boiler cannot be operated. It measures the temperature inside the boiler, being inserted into a blind dry tube in the boiler itself and gives the command to the boiler when to heat water, and when to turn off. And secondly, it is an outdoor temperature sensor. Why it is needed? I think many people know how it works, but if anyone is interested, I will tell you briefly. There is an automatic system that can be installed in a room that will maintain the temperature inside this room by giving commands to the boiler. There is even a portable one, like the Viessmann Vitotrol 100 UTDB. Seemed convenient. But which room to put it in? In the living room, kitchen, corridor, children’s room? Some people like to sleep in a warmer room, some like it cooler. The house faces all four directions. Somewhere bright sun and somewhere deep shade. Insolation even in winter’s clear sunny. But frosty days are such that the temperature difference between the south and north sides in the rooms is very significant. It is comfortable in the north, hot in the south. Either it is comfortable in the south, and in the north it is cool. What to do?? It’s unrealistic to put a sensor in every room. There is no such thing. In the end, the only option left is to do away with the internal temperature sensor and install thermostatic control heads on the radiators that automatically maintain the correct temperature in each room. And the hot water supply is carried out according to the scheme of the maximum required temperature in any room. And in the ones where it’s cooler, we just turn it down with the thermostat. But herein lies another snag. The boiler controls the return temperature. of water returning to the boiler and modulates the burner to reduce the amount of heat escaping if the return has become too hot. Hot return suggests that the thermal heads on the radiators are almost closed due to the increased temperature in the rooms and stop receiving hot water, which starts to go straight back to the boiler. But this is, for example, a sunny winter day. Come nighttime. Think back to last winter 2014/2015. It can even be thawing during the day, dripping from the roof, around zero. And at night it hits freezing at minus 20. Everyone is sleeping, the temperature is dropping. Thermostatic radiator heads open, the radiators fill with water, give off heat and the return flow is cool. What does the boiler do?? It sees the temperature drop and increases the burner modulation to the maximum supply temperature set by the user during the day. Like 50 degrees Celsius. He can’t set it any lower, it’s the default setting. What happens next? Then the residents of the house becomes cool at two in the morning and someone jumps up and squirming from the cold runs into the boiler room and increases the temperature of the outgoing water to 60 or even 70 degrees. Or maybe even up to 80. And so goes on almost every day. It is possible to set a high medium temperature at once. And hope that the thermoregulators will overlap after reaching the desired temperature. But, first of all, this is very uncomfortable. The radiators heat up and give “hard” heat. And it’s not even. And the boiler constantly turns off and on after a short time if it is warm outside. It is much more comfortable when the radiators are evenly warm than when they are either hot or off. At.Secondly, at high temperatures the boiler stops working in condensing mode and becomes just an ordinary boiler, which dramatically increases gas consumption. What to do? That’s why there is an outdoor temperature sensor, which alone gives the boiler a command to increase the temperature of the boiler water based on the temperature outside, regardless of what is set there by the user manually. For this purpose, the boiler has several schedules of temperature control, which can be selected by the user himself, based on his experience. It depends on different factors. From the number of radiators, their heat output, their needs, the presence of underfloor heating that is low-temperature (for example, the supply temperature to the underfloor heating is only 30 degrees enough to completely replace the radiators on the entire floor), etc.д. Usually the user knows very well at what temperature the frost he needs to set the boiler to. My curve, for example, “C”. And then one sleeps easy, because now the boiler knows when it is hot and when it is cold and increases or decreases the temperature by itself. This, by the way, also leads to a decrease in gas consumption. As it turned out, you can find sensors in companies that sell boiler equipment. And if we still have boilers in stock, the external ones are only available by order. But they’re expensive. For example, you can find a boiler sensor today for about this price. And the outdoor sensor costs even more. I opened the manual for service and repair, and, miraculously, it becomes quite obvious that the sensors are the most common thermistors. There is nothing else in them. What are they asking for?? This is the case when it is for the brand. Not only that, there are curves of resistance changes as a function of temperature. And we don’t need more than that. The thermistor is marked by the nominal resistance at 25 degrees. From the curves we see that the boiler sensor is rated at about 10 kohms, and the outdoor sensor. 5 Kohm. This will be a starting point for your search.In the description of branded boiler sensor we see a clue NTC sensor. Open the NTC datasheets and look for. NTC thermistors, as we can see, indeed, exactly match our curves. Boiler sensor. NTC-10K, external temperature sensor. NTC-5K. Look at the resistance at different points at different temperatures and you will see that. Looking for where to buy. In Chip and Dip do not have, there are 4.7 kV nearest and t. п. Let’s go on e-bay. Op-pa. From China you can get them as much as 350 for our money. And there are plenty of suggestions. Also sealed in airtight tubes, but with meter-long cords. Exactly the same one that looks like this will be in a bag marked Viessmann. You won’t find any difference in appearance or parameters. I did not want to wait two months for a parcel from China and found a closer, from Germany. expensive, but you can choose the length of wire. If for the boiler a meter or two meter cord is enough, then for the outdoor temperature sensor, in my case, to the street with a normal bend, required 6 m of cable. And what’s more, the thermistors here have a 1% error, not 5 as are common in the Chinese variants. You can see the prices. Your two sensors will cost 23 euros! Plus DHL shipping on the order of 13 for both. Total 36 euros in total against about 250 (120130) if you buy branded! Crimped, sealed, with silicone all-weather wires. I do not know the accuracy class of branded, but I’m sure that they will not be more accurate than 1%. And you don’t need more accuracy. So, who needs it, order it and you’ll be happy for a beer. Beforehand, check the manual for your boiler. Perhaps, in different years and for different models, the curve will be different. Therefore, refer to the service manual for your boiler model. They are always available on the manufacturer’s website.
Boiler temperature sensor replacement
The boiler stops switching on, and there may be no error on the screen (remote control);
If the temperature in the room or in the indirect heating boiler does not match the desired temperature, and the boiler does not turn on, it indicates a defect in the temperature sensor. The boiler is faulty, but the automation does not see the problem, because one of the faulty sensors shows it that everything is fine and there is no need to start heating. After conducting a diagnosis, the boiler temperature sensor that caused the problem is replaced.
The desired temperature of water or coolant does not correspond to the temperature produced by the boiler;
Temperature sensor is stuck in a certain position or sends a false signal to the electronic board. To determine the cause of failure will help diagnose the system. The master will carry out the necessary measurements and replace the boiler temperature sensor.
the boiler goes into error on one or the other sensor;
As the coolant heats up, the resistance of the temperature sensor begins to decrease, which tells the control system to perform a particular action. If automatics does not see any changes in sensor indications, and the process of heating the coolant is running, the safety system switches off the burner to avoid overheating. Accordingly, this prevents the occurrence of more serious breakdowns.
In the course of scheduled maintenance, the master should obligatory check the serviceability of all sensors. Accordingly, to make recommendations for the replacement of the boiler temperature sensor and warn the customer about possible problems associated with this failure.
How does the interaction between the sensor and the boiler
Depending on the boiler model, there are 2 ways of communication: directly and via a room thermostat.
Connect the temperature sensor directly can only be connected to the boiler models with this possibility (appropriate automation and terminal block / jack on the boiler), this feature is reported in the technical specifications model. For example, the ability to connect temperature sensors have such models as: line Baxi ECO Four, line Baxi LUNA-3, Buderus Logamax U072, Viessmann Vitopend 100-W and most other modern models of gas boilers.
Connection of the external control directly supports both electric and solid fuel boilers.
If the boiler has a simple automation with little function, it is better to connect an external sensor through an electronic room thermostat with the possibility of programming. Programming the boiler allows you to set the template of the heating system, for example, reducing the temperature to 15 degrees during working hours when the owners are not home, which will save significantly on heating, regardless of the type of fuel used. The cost of a good thermostat is about 1,500-3,000. but it pays for itself in a few months of operation if used properly.
An example of a room programmable thermostat (model. Teplocom TS-Prog-2AA8A).
Room thermostats already have a built in sensor that measures the temperature in the room in which it is installed. To realize a weather dependent control, you need to buy a universal outdoor temperature sensor. Thermostats that are already equipped with an outdoor temperature sensor are rarely sold. Often, however, a temperature sensor for underfloor heating is included in the delivery set.
In general, the organization of the optimal scheme of control of the heating system is sufficient three sensors for temperature: external room, outdoor and floor heating.
In what place to install
The thermostat is set very close to the monitored parameter. So in two-circuit boilers, they are placed on the return before entering the boiler, at the outlet of the boiler in the supply pipe, at the outlet of the unit in the circuit of DHW.
The sensor for monitoring the flue gas return temperature is installed at the boiler outlet in front of the chimney mouth. Wireless DT for a boiler unit are placed directly on the controller or on the gas shutoff valve. Wired. connected in the way, indicated by the manufacturer of the equipment.
Principle of sensors operation
Thermostats, as well as programmers, essentially work on the same principle. You set the temperature threshold below which the boiler heating is switched on. The only difference between the devices is their threshold, which depends on the quality. Chinese analogues of famous devices, as a rule, have a longer threshold of operation than the European original.
Threshold of one degree is considered as a norm. For example, if you set the temperature maintenance at 20 degrees, then the normal threshold, when the temperature drops below 19. the boiler will work. And when the temperature rises above 21, it shuts down.
Chinese counterparts have a spread of up to two degrees or more, which accordingly affects the quality of the burner. At the same time more expensive and higher quality models from European producers can have an error of only 0.2 degrees for example.
NTC sensors.
In boilers they are used to measure the temperature of the coolant, hot water temperature, indoor and outdoor air temperature, etc.д. Consists of a semiconductor element (5 retail), a housing and a connector. They differ in temperature response, housing shape and connector type. Basic function. to change the electrical resistance depending on the temperature. The higher the temperature. the lower the resistance.
Sensors designed to measure the temperature of the coolant and hot water are immersion and surface-mounted. The immersion sensor is placed inside the pipe, is washed with water and reacts the fastest to temperature changes. Overhead sensor is attached to the outside of the pipe and does not contact with water directly. This results in times longer lifetime of the overhead sensor.
Viessmann Vitopend boiler NTC sensors (there are fakes)
The most common sensors are NTC (used by many boiler manufacturers), in most cases interchangeable (you can buy just by likeness, many fakes sell both normal quality and horrible. Poor quality fake housing can rot in six months to a year).
NTC overhead sensor. Because it is not in direct contact with water, the service life of a cheap counterfeit sensor can approach that of an expensive branded sensor.
The clamp-on sensor is not as responsive to temperature changes.
