What is a temperature switch?
Temperature switches, commonly referred to as thermal switches, are used to open and close switch contacts (thermostat). Depending on the input temperature, the switching status of the temperature switch changes. In order to safeguard against overheating or overcooling, this feature is employed. In general, thermal switches are used to control temperature and to monitor the temperature of machinery and equipment.
How do you calibrate a temperature switch?
Purpose and Scope:
This procedure includes instructions for calibrating a temperature switch using a thermometer and a dry bath temperature calibrator. The procedure includes these directions.
Tools required for calibration
- Necessary hand tools.
- Dry bath temperature calibrator.
- Fluke digital thermometer.
- Standard thermocouple.
- Soft cloth for cleaning.
- Thermocouple sockets, Test Probes & Leads
- A temperature switch will stop working properly, stop producing output, and stop activating the system if you unplug it from the system to which it is connected.
- This might result in problems or failures in a system where the temperature switch is an essential safety feature that aids in preventing damage or accidents from occurring in the system.
- For information on fundamental safety, general guidance, and specifics on calibrating operations in process industries, please click on the link given below.
Process Industry Calibration Process: Basic Safety and General Aspects
- Whenever you need to disconnect a temperature switch for maintenance or repair, make sure you follow the right processes and take the required precautions to avoid any accidents or system damage. You risk seriously hurting yourself or others if you don’t comply. has the potential to have an adverse effect on the system, resulting in problems or failures.
- Ask the panel operator to choose the manual mode and MOS for the control loop and the temperature switch ESD loop.
- Disconnect the power to the process equipment: Before attempting to remove the temperature switch, be sure that all power to the apparatus or process has been turned off.
- Give the process being monitored some time to cool off if it is operating at a high temperature before attempting to remove the temperature switch. As a result, there will be less chance of burns or temperature switch damage.
- Remove any attachments: If the temperature switch is linked to a fitting or other component, carefully remove any bolts, clamps, or other fasteners that may be holding it in place.
- Release the temperature switch from any fasteners, then unplug the wires that attach it to the measurement device. Avoid causing any cables or connections damage.
- Make sure the temperature switch is completely isolated from the operation.
- Use the proper PPE, such as gloves, safety glasses, and a face mask, when working in a process area to protect yourself from harmful chemicals and to adhere to safety regulations.
- The temperature switch signal wire should be completely separated from any nearby junction boxes or marshalling panels near the control room with the help of an instrument loop diagram.
- And make sure to get instructions from a qualified professional or the equipment’s guide on how to remove the temperature switch from the equipment appropriately.
- Storage of temperature switches must be done properly. When the temperature switch is removed, it should be stored safely away from dangerous components.
Tools for calibrating and validating temperatures include dry-blocks. For heating or cooling temperature sensors, such thermocouples or RTDs, to known and accurate temperatures, they offer a stable and uniform environment. This makes it feasible to calibrate and test temperature-measuring equipment.
Temperature switch calibration setup
- Collect the required equipment, including a dry bath calibrator, a thermowell of the right size for a temperature switch, a thermometer with the appropriate range and accuracy, a power source, a standard thermocouple, and the probes and connectors needed to attach the temperature switch to the calibrator and thermometer.
- Ensure sure the temperature switch and calibrating test equipment are clean of any debris or residue that might affect the calibration’s precision.
- Plug the dry bath calibrator into an electrical socket to turn it on.Verify the correct operation of the dry bath calibrator and the accuracy of the temperature control.
- As you place the temperature switch into the dry bath calibrator with the suitable thermowell, make sure the sensing element is entirely submerged in the bath and not touching the walls or bottom of the container.
- While engaging in any thermowell-related activity, it’s critical to adhere to adequate safety precautions and use the correct personal protective equipment, such as suitable gloves and eye protection.
- Connect the temperature switch to the multimeter in continuity or resistance mode using the appropriate probes and leads. Verify the leads, probes, and temperature switch are in fine shape, and that the connection is stable.
- To measure the temperature of the dry bath calibrator, insert the standard reference thermocouple with a standard thermometer in the same location as the temperature switch. Verify the thermometer’s accuracy and resolution to ensure they are appropriate for the calibration process and that it has been calibrated.
- The temperature displayed by the dry bath calibrator should be compared to the reading from the standard thermometer.
- The setup is ready for calibration of the temperature switch if the thermometer and dry bath calibrator are steady and the temperatures coincide.
- Before making any adjustments, check the current settings of the temperature switch to make sure they are already within the proper temperature range.
- Verify that all of the connections are correctly secured.
- By referencing the instrument data sheet, you may verify a number of temperature switch parameters. Typical settings are the tag number, type, number of contacts utilized, setpoint, and reset values.
- Turn on the multimeter and choose either the resistance or continuity mode. Adjust the dry bath temperature calibrator step by step increments to the temperature switch set point.
- Never go above the temperature range of the temperature switch; always read the handbook to find out the precise range.
- Increase the temperature gradually until it is within the operating range of the temperature switch, then wait for it to stabilize.
- The temperature should be ramped up across the nominal operating range of the temperature switch very gradually.
- The temperature should be recorded using a normal thermometer whenever the output of the temperature switch changes state (from the specified setpoint).
- Gradually ramp the temperature in the opposite way until the temperature switch changes the state (reset point). Record the temperature that a typical thermometer displays.
- Compare the readings acquired during calibration to the expected values of the temperature switch. If there are significant variations, adjust the temperature switch as necessary.
- Make small adjustments and check the temperature measurement after each one to make sure you are not crossing over the appropriate set point.
- Adjust the temperature switch setpoint until the required temperature is reached for the switch contacts to open and close.
- Before beginning, please read the manufacturer’s instructions since the calibration process may be different depending on the specific temperature switch.
- Apply inputs that correspond to the temperature switch’s set and reset points in the direction of temperature changes from the test standards five to six times to verify the repeatability of the temperature switch.
- If the output contact change over the value of the temperature switch does not fall within an acceptable range, calibration is required.
- Again, if the output contact change overvalues exceed the permitted range, the temperature switch has to be repaired or replaced.
- There is no need for additional calibration if all of the output contacts change over values (+/-%) fall within accepted limits.
- The output contact change over values should be recorded in the blank calibration report’s as found/as left column.
- An example temperature cycle during temperature switch calibration is shown in the above graph.
- To capture the set and reset points, gradually ramp the temperature up and down over the calibration range after fast reaching a temperature point that is near to the calibration range at the beginning.
- Three calibration cycles were performed in this sample to record the switch’s repeatability.
- You may quickly return the temperature to room temperature after calibration.
Completion of calibration
- When the calibration has been successfully finished, attach the calibration label on the temperature switch.
- When the calibration is complete, clean the apparatus, store it somewhere safe, and make a note of the temperature switch calibration data for later use.
- The thermowell should be carefully removed without damaging nearby equipment.
- The dry bath calibrator should be disconnected.
- Return the temperature switch in the processing area to its original position.
- Make sure the calibration area is clean.
- De-isolate the apparatus.
- Return the temperature switch’s bypassed or inhibited signal to its usual level.
- Make sure the temperature switch is working properly before returning it into use.
Sample calibration report
The following image demonstrates how the temperature switch sample report of calibration was carried out using a dry bath temperature calibrator and a standard thermometer, with a standard thermocouple serving as the reference.
You can get the Excel template that was used to construct the temperature switch calibration report by clicking the link below.