Temperature Sensors and Their Location

The temperature monitor has become an important part of the specification of a refrigerated delivery vehicle and nowadays virtually all operators of vehicles carrying chilled or frozen foods will ask for a temperature monitoring system to be fitted to any new vehicle they acquire.

Increasingly these systems are microprocessor based electronic units rather than the more basic chart recorder types that were popular for many years. However, regardless of the type of system preferred by the user, the essential objectives of taking and maintaining temperature records are the same.

The most effective method of air temperature monitoring is the permanent fitting of two sensors in the vehicle chamber. One should be positioned below the cooling unit to measure return air temperature, and the other in the ceiling of the chamber about three quarters of the way down the length of the chamber.

The sensors are connected to a suitable recording instrument which is permanently fitted to the trailer or vehicle cab. In the case of a cooling unit which does not used forced air, the air temperature should be measured above and below the load, in order to take into account likely vertical temperature gradients.

Multi-compartment vehicles are designed to carry food at differed temperatures in different compartments. Air temperature measurements should be made for each compartment so that the performance of each can be confidently assessed. If only one sensor is installed, then it should be positioned to measure return air temperature.