How To Check A Thermostat

[MANATEC]

We are using a 110C thermostat in our application. How do we check the thermostat during incoming inspection


Regards,

Manatec

 

[rjvh]

What is a 110C thermostat (a type) or a device that switch at 110 degree celcius???

and what do you mean with incoming inspection

what do you want to inspect??

if you want to check if a general thermostat is working than you measure the output and try to manipulate the device with heat or cold and look if you have a switching signal or a analoge output signal that varies during the different temparatures

hope this helps as that the info you give is limited and not so clear for interpetation

Robert-Jan

 

[MANATEC]

Thermostat we are using cuts off at 110c when used in the application. We want to check it at our incoming stage. What are the parameters to be checked ??

Regards,

Manatec

 

[rjvh]

Thermostat we are using cuts off at 110c when used in the application. We want to check it at our incoming stage. What are the parameters to be checked ??

Regards,

Manatec

Incoming stage of what??? is it a process what you try to control ???

Cuting out on 110 degree celcius is the level of steam under slight pressure

Robert-Jan

 

[bassnut]

If its a resistance thermostat, measure incoming stock resistance at 110c, if its a switching type, same trick, check switching at 110c, seems simple. A small oven operating at 110c you can easily insert sensors for testing seems obvious. If you dont want to do that, and its a resistance device, measure its resistance at ambient, although this wouldnt be as reliable as at the operating temp.

 

[ericgibbs]

A domestic hair dryer will raise it to 110Cdeg, use a simple mercury thermometer.
Whats the operating temperature tolerance.?

 

[stevez]

There are a number of things that I might check. It's not clear but you've provided clues that you have a thermal switch that opens at 110 degrees C. If that is correct then I'd suggest:

Create a fixture that will impose a load on the switch that represents a reasonable test of the contacts. While you may not need to fully load the contacts I'd use more than microamps to test a contact rated at an amp or more.

The fixture would include a means of heating and cooling - or heating the switch so that it can cycle from closed to open on heating past the expected setpoint. Measure the point where it opens - then again where it closes on cooling. There should be some difference between the open and close points. You might then compare your test results with manufacturer's specifications for trip point and differential.

Be careful of noting the rating for the number of cycles - some devices are made to operate only on occasion and repeated cycles can wear the switch out. An example might be a high limit stat where it is only there as an emergency protective measure.

 

[xanadunow]

There is just not enough information provided in the query to provide satisfactory answer but I will try.

Note that thermostat is an adjustable device, whilst the thermal cut-off switches are the NC (normally closed contact) devices that open their contact once the predetermined (by the manufacturer) temperature is reached and they do come in two varieties; resettable (i.e. the contact will close again once the temperature drops below the specified) or non-resettable (i.e. it acts like a "fuse" - once the predetermined temperature is reached it does blows like a fuse and does need to be replaced by another one).

If it is a thermostat (i.e. an adjustable device), then the easiest way to check or calibrate it, is to use the boiling water after having it (the thermostat) set to 100 deg Centigrade, this is when the water boils (+/- the error due to atmosferic pressure). Have the thermostat set to more than 100 deg Centigrade and insert its sensing part into a pot in which the water will be slowly brought to a boiling point.

Make a simple circuit consisting of a battery and a light bulb that will draw approx the rated current of the contacts your thermostat was designed for. Have those contacts wired in series with the globe and battery. You may need to use an extra resistor in series to ensure the current drawn by the bulb does not exceed the rating of the thermostat's contacts. The Ohm's Law will give you the answer required.

The globe will stay on untill the temperature set on the thermostat's scale is reached. The 100 deg Centigrade is the easiest to determin because this is the temperature at which the water boils at (remember the error I did mention earlier? It would be negligible, assuming you do not live on Mt Everest).

Once the water boils, start backing off the thermostat setting (a fraction at the time) until you find the point when the contacts open and the bulb's light goes out. Now, mark that point on your thermostat's scale. This is the 100 deg Centigrade point - it should correspond to the 100deg temperature point on the dial of the thermostat. If you can adjust the position of the scale to read exactly 100 degrees C without changing the adjustment of your thermostat - do it now. This way, your thermostat becomes calibrated at 100deg Centigrade.

You can repeat this exercise as many times as you need until you are happy that 100 degrees set on the thermostat's dial coresponds to the point in time when water starts to boil and the light goes out.

You can assume now with reasonable degree of comfort that your required 110 deg position on the thermostats scale is also accurate because you have just calibrated it at 100degs C.

Now, to make a more elaborate testing you can try various settings of the thermostat, while monitoring the water temperature in the pot at other than boiling temperatures using thermometer of a reasonable quality and accuracy as your temperature reference.

As a point of interest, note that thermostats are not very accurate devices and their setting has a built in error i.e. if the contacts open at the 100 degrees setting and the light goes out, they will probably not close up again until the temperature drops to about 98 degrees or so. This lagging effect is called hysteresis and you can "google it" on the net to your content

Regards,
xanadunow