---

Process Scanner and Temperature Calibrator

Temperature Measurement and Control

These are documents and circuits which will help learn Basic Temperature closed loop control, There are many ways to control temperature.

System for Industrial Controls

• ON-OFF Hysteresis or Dead Band Control.
• Proportional Control with Reset.
• Full PID Control, Manual and Auto Tune.

The first one is an electronic emulation of Thermostat or Electro-Mechanical Controls. The second is Time Proportional like a slow PWM. The third is the complete adaptive control.

While the first is like a limit switch, the second works like a SMPS, the third PID takes into account the speed of the process and dynamic changes or disturbances of the system and compensates in real time.

Example - In a Oven, one batch may have 100 metal boxes to heat, the second batch may have 10 boxes, the door may be frequently opened and the mains power (heater) may be fluctuating. A system that is able to adapt to these changes, without much readjustments is the objective of an ideal process control. The Accuracy and the Energy efficiency being the most important.

Multizone Process Scanner

This could take current or voltage inputs from many remote transmitters, 4-20mA or 0-1 V Inputs. Then it would display the calibrated value in a LED display. The Zone number was a digital display. This serves as a monitor of process values. It had a analog output with a digital channel byte-word output for interface with other instruments.

This uses the CD4051-52 for the analog switching. Operating this at +/- 7.5V gives best isolation from channels and low ON resistance. Now you have many types of devices to do this.



When a large area or object has to be heated, many heaters are used. This device can monitor and display the temperature at various points. The Operator then can make adjustments in heating or cooling so that he can maintain Uniform temperature or a Temperature Gradient as specified by the Process.

Process Control Education - Instrumentation

There are many ways, these scanners are used. Many different parameters like pressure, temperature, level are measured with different sensors and converted to a 4-20 mA level using transmitters for each sensor. Then many parameters can be measured in one equipment, when it needs only periodic attention. As the scan rate can be set from 1 to 50 seconds, the operator will be able to keep a tab on the values or record it. This reduces the real estate required on the control panel. Then the control room can be small, as it has to be at a vantage point, with a birds view of the entire factory floor.

Temperature Calibrator for RTD and Thermocouple

This is a Milli-Volt and Milli-Amp Source for Calibration of Temperature Measurement and Control Instruments using Thermocouples. There is also a Passive Variable Resistance Source for Simulating a PT-100 RTD Sensor.

This calibrator was a simple solution i built. This instrument itself was calibrated by Instruments like the Calibrators from Omega which are the best you can get.

Read More

• Temperature Measurement and Control
• Industrial Process Control Circuits

Back to Process Control Instrumentation