If you are towing a trailer up a steep Arizona grade in July, will your car overheat? If you are driving on the interstate in North Dakota in January, will your windshield fully defrost? You normally do not even think of these questions because your vehicle HVAC system has been carefully tested and optimized long before it has been put into mass production. HVAC testing in automobiles requires the monitoring of hundreds of temperature points on the engine, radiator, air conditioning system and passenger cabin. Only a short test season is available to do this. Using a compact, portable and accurate data acquisition system is a necessity.

Temperatures in vehicle testing are measured with thermocouples. Thermocouples are simple, rugged, have a wide measurement range, and are small so they can be used anywhere in the vehicle. Thermocouples have some complications, however, when used with data acquisition systems. High amplification, linearization and reference junction compensation are needed when working with thermocouples. A single reference junction temperature sensor often leads to substantial errors in vehicle testing because the junction of each thermocouple input may be subject to a different ambient temperature.

The ideal thermocouple data acquisition system for vehicle testing is compact, can accept hundreds of inputs, provides reference junction compensation for each channel individually, and operates on vehicle power. In addition, the system must linearize the thermocouple readings into degrees, and interface easily to a data-collection PC.