1How is a bimetal designed and constructed?
Two dissimilar metals with different expansion rated connected together at least on the ends
2Flat straight bimetals produce thermostats with slow opening contacts. (T or F)
True
3Disc type bimetal construction produces a thermostat with a snap action contact operation. (T or F)
True
4How must bimetal operated thermostats be installed?
Tight to a clean surface
5What is the key ingredient in the construction of a bellows expansion thermostat which allows it to operate so accurately?
A type of refrigerant or liquid like mercury with a constant rate
6Mercury filled diastat assemblies are used on what temp. range thermostats?
High temp
7How can you tell if a thermostat is rated for pilot duty or power duty?
Pilot duty is rated in VA or amperage less than 1 amp
8What does the suffix "KX"stamped on the side of the EA model thermostat indicate?q
Pilot duty
9 What does an electrical rating expressed in "VA" on the side of a thermostat indicate?
Pilot duty
10When checking the contacts in a thermostat, what would you be looking for that would indicate that the thermostat needs to be replaced?
Contacts cratered out or worn very thin, or welded together
11Thermostats made with copper diastats are normally used for what applications?
Water
12Thermostats with steel diastats are normally used for what applications?
Ovens and ranges
13Nickel plated diastats are used for what thermostat applications in the foodservice industry?
Fryers
14What is the switching arrangement on a Robertshaw EA thermostat?
SPST
15What is the switching arrangement on a Robertshaw SJ model thermostat?
DPST with only one set of contacts that style
16Do all of the contact sets on a SJ model thermostat cycle with changes in the temperature?
No
17Many manufacturers are changing some of their thermostats from "D" model to "SJ" model Robershaw thermostats. What must you be very careful of when making this conversion?
The wiring is totally different on the thermostats
18Robertshaw "H" model thermostats have a reset button that must be pushed every time the thermostat is tuned off and back on, as well as anytime the temp. setting is lowered more than 15 degrees when used in liquid and 30 degrees in air. (T or F)
True
19Robertshaw's LCC and LCH model high imit thermostats are different from all previous models because they are considered to be what?
Fail safe
20If the diastat would break off of a Robertshaw LCC or LCH limit thermostat, which way would the control fail?
Opposite of its normal operation
21The surface the bimetal thermostats or diastats must be fastened to to; must be in what condition?
Clean
22If the bimetal thermostat or a diastatic is not fastened tightly to the surface, what will happen to the temp. controlling ability of the thermostat?
Erratic behavior
23When you have completed the installation of a new thermostat, what must you check in relation to the capillary tube?
Make sure it is not routed near any electrical connections
24If the thermostat is installed in close quarters, what is it advisable to do with the capillary tube of the thermostat?
Insulate it
25If a thermostat fails and you inspect the inside of it, you find the bellows is fully expanded, what must you look for before energizing the equipment with the new thermostat installed?
A stuck contactor or gas valve
26Erratic heating problems tracked to the thermostat in pilot duty applications are often tue to what problem in the thermostat?
Contacts that have minor dirt or oxidation build up on them
27Welded contacts in a thermostat indicate what?
A short circuit in the load
28How many times should you attempt to calibrate a thermostat?
Once
29After a thermostat has been calibrated, what should you do, and why?
Paint the adjustment screws with nail polish to lock the adjustment threads
30Solid state temp. controls have reduced temp. differentials to the range of how many degrees?
1 or 2 degrees
31What are the three components needed to produce a solid state temp. control?
Sensor, control board, and potentiometer
32What are the three different kinds of temp. sensors that can be used with a solid state control?
Thermocouple, thermistor, and RTD
33What occurs when a thermocouple sensor is heated?
It changes resistance or millivolt output
34Which kind of sensor works well even into extremely high temps. and can stant up to rugged applications?
Thermocouple
35What happens to a RTD sensor as it is heated?
The resistance increases
36What happens to a thermistor as it is heated?
The resistance will fall if it is a NTC sensor and rise if it is a PTC sensor
37which is supposed to be a more accurate sensor, a RTD or a thermistor?
RTD
38What is an "NTC" thermistor?
Negative temp. Coefficient
39Why are thermistors the most popular of all of the temp. sensors?
Less expensive
40How do you test the performance of a thermocouple?
Compare the temp. at the sensor to the millivolt output and compare it to a chart for that thermocouple
41How can you test a RTD sensor?
Check resistance with a digital meter and compare it to a chart
42How can you test a thermistor?
Check resistance with a digital meter and compare it to a chart
43What kind of meter must you used to check a RTD or thermistor sensor?
Digital Ohmmeter
44How do you check the operation of the potentiometer?
Use an analog meter and make sure the needle moves across the scale smoothly at the shaft is turned.
45can you test the solid state temp. control module?
No
46The output voltage from a solid state temp. controller or computer is often DC volts. (T orF)
True
47Proper testing of a RTD or thermistor can only be done with what kind of meter?
Digital ohmmeter
48Accurate testing of a potentiometer can only be done with what kind of meter?
Analog meter
49How does a solid state controller keep from overriding the set temperature?
Starts to cycle on and off as it approaches the set temperature