Blog post by Joe Palace, Senior Electrical Engineer
Good common practices and tips when using a Siemens PID Temperature Technology object to control your heat device inside of your Siemens PLC program.
- Before doing anything, you want to pick the correct thermal device that will be used to measure the temperature device. Is it a thermal couple, a thermistor, a resistor? With that, set up the correct parameters and units (Fahrenheit or Celsius). This is found in the analog card properties, under the Hardware device configuration
- Set the Cyclic interrupt, OB30, to a reasonable interrupt time, 100 – 500ms
- Your technology object, the PID FB, should always be enabled
- Before starting the tuning algorithm, determine what tuning mode will be used
- Pre-tuning – used if the temperature difference between actual and setup temperature is greater than 20 degrees
- Fine Tuning – used when the temperature difference between actual and setup are within a few degrees
* Note: You might want to manually start the PID to start warming up the device before switching to Pre-Tune or Fine Tune. Set tuning mode to Manual
- If you have multiple PID loops and the devices that are being controlled are similar, you can manually enter the PID values from a device that has already been tuned
- This is found under the Advanced Settings section in the configuration folder for your technology object
- Have a way to shut down the heat device if necessary, in case of a malfunction. In such a case, a heat switch button (externally wired or on the HMI) to enable the heat device(s). This way if the PID loop goes awry, you won’t run the risk of melting a part or burning up a heating element
By following these simple steps will save you time and prevent any headaches in setting up your PID loop to control your temperature device.
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