For investigations involving fires, explosions, or water damage; testing of thermostats and temperature controls can provide valuable information on whether a device malfunctioned, or what the state of a system was prior to the loss. Adjustable thermostats can be tested to determine how the set-temperature corresponds to the actual temperatures at which the switch opens and closes. A non-adjustable temperature switch can be tested to see if it responds according to the design specifications.
In order to perform these tests, the thermostat needs to be subjected to a controlled environment that changes in temperature across the setting range of the thermostat. The response of the thermostat switch to temperature change can be monitored by taking electrical measurements across the switch. Setting up such a test poses several technical challenges.
The rate of temperature change needs to be slow enough to ensure that the test subject is always at the same temperature as the surrounding environment. If the rate of temperature change is too fast, the measurement of the environment’s temperature won’t accurately reflect the actual temperature of the thermostat mechanisms. It’s standard practice to keep the temperature change rate at 2 °F per minute or slower during the test. Controlling the temperature during a heating cycle can easily be accomplished with electric heaters. However, controlling the cooling portions of the test requires more specialized equipment.
At Synergy, we use a Sun Systems EC1A programmable temperature chamber to test thermostats and controls. The EC1A is capable of testing items at temperatures anywhere between -163 °F and 600 °F. It’s cooled by a connected tank of liquid carbon dioxide, which is injected into the chamber in precise amounts. The wide operating range and ability to program different types of tests make the EC1A an excellent instrument for testing thermostats and thermal controls. When all of the test data is output and recorded by our Fluke 2680A data acquisition system, the process is further streamlined. See the chart below for an example of the results that can be obtained with our testing system. This test was started at a temperature close to room temp, then the chamber was cycled twice between 65 °F and 20 °F. The graph shows that the Normally Open (N/O) thermostat switch closes at 28 °F upon cooling, and opens at a temperature of 37 °F upon heating. For this thermostat, the set temperature and temperature differential of 9 °F indicated normal operation.