Testing av temperaturbrytere og kontrollere
De fleste temperaturkontrollere har en form for justering med demping og PID (proporsjonal-, integral- og derivatverdier) for utjevning av den målte prosesstemperaturen, noe som reduserer sikten.
Bryterteknologi kan være forvirrende. Få mer informasjon, finn ut hvordan du utfører tester og få tekniske tips under:
Fordeler med testing av temperaturbrytere og kontrollere:
- Spar tid i felten.
- Sikre nøyaktige og reproduserbare testresultater.
- Øk prosesskvalitet og brukersikkerhet.
Temperature switch and controller testing in the field
Temperature switches and controllers are commonly used in small processes and in control loops where a programmable logic controller (PLC) or larger distributed control system (DCS) are not warranted.
Temperature controllers provide both switching capability based on rising and dropping temperatures, as well as a local indication of the measured temperature.
Most temperature controllers have some form of tuning, using damping and PID (Proportional, Integral and Derivative values) for smoothing out the measured process temperature, reducing variability.
The terminology around switches can be confusing. The set state of the switch is the action the switch takes when an input stimulus above or below a specified value is applied. This stimulus can prompt an action such as closing a switch, which in turn starts or stops a motor, or opens and closes a valve. The reset point is considered the relaxed state of the switch, which is typically referred to as “Normally Open” or “Normally Closed.” This describes the default condition of the switch. Lastly, deadband is the band of temperature equal to the difference between the temperatures where a switch sets, and resets. See illustration.
To perform the test:
To use a thermocouple simulator to test a switch with a thermocouple input:
Disconnect the process measurement sensor.
Connect the mini-connector from the test wires to the TC source connection of the calibrator (figure above).
Connect the calibrator resistance measurement terminals to the switch contacts to measure continuity.
Set the calibrator to source/simulate the correct thermocouple type and to measure resistance.
Configure the calibrator for the switch test describing the expected setpoint temperature, allowable deviation and expected deadband values.
Run the test and evaluate the test results.
Adjust the switch as needed and repeat the test, confirming that the adjustment was successful and the switch is performing as expected.
- When testing the temperature switch, the applied temperature should agree with the temperature displayed on the controller or switch’s display. If it does not agree, the device’s input A/D may need adjustment per manufacturer’s procedure.
- When testing a switch with damping (delay of output change for a change on the input) set, it might be necessary to test the switch manually by slowly changing the temperature in small tests.
- When testing a mechanical temperature switch (no external sensor), use a field temperature bath calibrator for best results.
- To test live switch contacts switching 24 V dc or 120- 240 V ac, select a calibrator that can measure these live voltages, such as the Fluke 75X family of Documenting Process Calibrators. Most other temperature calibrators can only measure continuity changes when testing switches.
Klikk her for kalibreringsprodukter>>