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.
- 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.
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.
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