Thermostats are necessary in managing the temperature of electrical panels and are usually combined with other devices, such as a fan or a heater. But which one to choose for your application?
Thermostats with single normally open contact (NO)
Fandis normally open single contact thermostats are recognizable at a glance, thanks to the BLUE knob and are useful, as the color also suggests, for managing ventilation or cooling systems in general.
The definition of normally open contact (also abbreviated as NO) could lead to some doubts about its interpretation: the contact is defined as “normally open” when the temperature of the surrounding environment is lower than that set and therefore the connected cooling, such as a fan, remains switched off. Let’s assume, therefore, that the room temperature rises: when the temperature exceeds the value set on the knob, the contact closes (close on rise), turning on the fan.
Thermostats with single contact normally closed (NC)
The second type of Fandis thermostat is the one with a normally closed single contact and can be recognized visually by the RED knob. It is used to pilot the switching on or off of heating systems, such as anti-condensation heaters.
In these thermostats, the contact is “normally closed” (also abbreviated to NC) when the ambient temperature is lower than the one set on the knob and consequently the connected device (for example an anti-condensation resistance) is active because it is necessary to heat.
Consequently, the room temperature increases until it reaches and exceeds the set temperature value, at this moment the contact opens (open on rise) switching off the anti-condensation heater.
To summarize, in our range:
- TRT-10A230V-NO: Thermostat with BLUE knob with Normally Open (NO) contact, close on rise (the contact closes as the temperature increases);
- TRT-10A230V-NC: Thermostat with RED knob contact Normally Closed (NC), open on rise (the contact opens as the temperature increases).
Both models are available with degrees in °C or °F.
The reverse logic
A very important note: sometimes it happens to receive reports from customers who complain about the incorrect functioning of the thermostats, for example that the NO purchased works like a NC.
All Fandis thermostats are tested one by one before leaving the production line, therefore, the reason is almost always in the method used to test their operation: in fact, it often happens that a the position of the knob is changed to verify activation of the connected fan or resistor.
In reality, in doing so it obtains an opposite result (reverse logic), thus reinforcing the idea that the thermostat purchased is not the correct one.
How to check if a thermostat is working
For correct operation, the value that must change is not the temperature set on the knob, but the environment temperature. Otherwise, all the operating logic, as already mentioned, is reversed.
To test a NO thermostat (blue knob), the best method is to set a temperature value on the knob that is higher than the ambient value and do not change its position. At this point, the connected fan is off.
With any source of heat (for example a hair dryer) heat the air surrounding the thermostat, when the ambient temperature exceeds the set one the fan will turn on.
In the case, however, of an NC thermostat (red knob) we will have to cool the surrounding air, perhaps by placing the thermostat in a refrigerator or by hitting it with cold air from an air conditioner, without ever changing the setting of the knob.
The same logic can be extended to the Orangis range, such as our TRT2 double thermostats and the IGR35F hygrostat, even if in the latter case the variable is represented by the relative humidity and having an exchange contact (NO+NC) the problem is less felt.
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