Troubleshooting Temperature Controllers

We often get calls for troubleshooting temperature controllers. Here are some tips that can save you some money and time.

My Field Service Technicians and I frequently are deployed to customer sites for “Failed” temperature controllers. There are numerous brands of temperature controllers in the market. Applications range from ovens to extrusion machines. Yet most temperature controllers share the same common functions. When troubleshooting temperature controllers, here are a few tips from a guy like me who’s done it plenty of times.

Usually, the actual temperature controller is NOT the problem. Temperature controllers normally have one or two control outputs to adjust the process temperature: A heat inputand (if required) a cool output. The temperature controller also may have outputs for alarms. The temperature outputs normally control relays (solid-state or conventional) or contactors. This is because the temperature controller outputs are either low voltage DC or 120VAC and the heaters or fans require high voltage 230-460VAC.

Solid state relays are preferred because of the numerous switching (On/Off) as the unit tries to maintain temperature. A simple method of determining why a unit is not maintaining temperature is to look at the display on the controller.

Normally, Output 1 is assigned to Heat and Output 2 is assigned to Cool. As the unit is started up and a temperature higher than the “Process Value” is set, you should see Output 1 come on (Unit is calling for Heat). This should continue until the unit reaches the “Set Value.” At that point, Output 1 should go off (plus or minus 5-10 degrees). Output 2 (Unit is calling for Cool) should come on if the Process Value exceeds the Set Value and go off once the Set Value is reached (Plus or Minus 5-10 degrees).

If this is happening, the next place to check is on the actual item being controlled (relay or contactor). Observe the relay/contactor to see if it is actually operating when the output is on (normally, relays have indicator lights and contactors can be checked visually).

Also, check the input and output high voltage going to the relay/contactor. If this checks out good, then the problem lies in either the actual heating element or the fan. For heating elements, a continuity check of the element normally will tell if it is open (bad).

Hopefully these simple checks can help you when troubleshooting temperature controllers and have your equipment back in operation faster. If not, our field service team is always standing by to assist.

Lonnie Gillilan is the Dallas field service manager for Innovative-IDM. You can reach him at [email protected]