Thursday, July 31, 2008

Build your own Meters and Instruments

These are basic measuring circuits you can build for your home lab.

I have documented a lab DMM i had built for my use many years ago. the circuits may have errors, build it only if you understand.

Analog Dial AVO Amps-Volts-Ohms meter

This was designed, keeping in mind, that sometimes we have few components available and we could be flat broke. Even that you could not carry your DMM somewhere, but you have to make some instrument for a quick need with what is available. If you are out of cash or feel like Robinson Crusoe, then this is a low cost measurement system. I designed it to practice on eagle, i am not sure how this circuit may work, it is not tested . But i have built, repaired and designed many DMMs. So there is a fair chance, parts of it may work :~) - Low cost Dial AVO meter

Auto ranging 4-1/2 digit digital voltmeter using ICL7135 of Intersil.

Tuesday, July 01, 2008

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 a 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.

Process control Application notes

  • Temperature control in plastic injection molding
  • Cooling Temperature Control
  • Capacitor Temperature Monitor


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