Instrumentation and Automation – 02

In Test and Measurement and Industrial Process Control a common factor is instrumentation. The measuring aspect is common to both. T&M instruments are used in Testing, Research, Automated Testing, Troubleshooting and Servicing. Process control Instruments are used in Production Lines made of Machines in a Factory. It could be Counters and Timers used for Textile or Steel Industry. It can also be Temperature and Pressure Controllers used in Oil Refining or Food Processing. So you see a difference. We have handheld Test Instruments like DMM and Scope and We have Handheld Instruments for Gas Monitoring or Humidity too. In automated testings we have rack mount test instruments. In Control panels we have Rail Mount carrying DIN standard Instruments.

  • On-Off controls or level trip relays can oscillate if hysteresis dead band is very small or absent.
  • Hysteresis is like on at 300 off at 304 like in heaters or air conditioners. If you on-off at sharp 300 there is a chatter or oscillation. This is called dead-band in temperature control. In above example 304-300=4 is the dead-band.
  • LF356, TLO71 and CA3140 are FET input Op-Amps, the bias is in pA, The caps for sample hold with these opamps are low leakage ones.10uF tantalum for long time, low resolution data. Long hold times with 12 bit data (analog) use 1uF plastic multilayer and clean-IPA + coat PCB with epoxy.
  • Design the product in such a way that neither the pot terminals or pot switch is used for mains voltage, instead use the pot switch or variable resistance for signaling and the mains can be switched with Relay or Thyristor.
  • If you need a 10.00K resistor 0.1% and you only have 1% in the market, you can trim lower values to higher values by removing the paint of the resistor and scratching the black metal film till you get the desired value. (this is only for testing or prototype development, R&D, not for manufacturing).
  • 7107 and 7135 of Intersil can be tested in-circuit, check Vref for 100mV or 1V reference, then short Vin and Vref the reading should be 1000 counts for 7107 and 10000 counts for 7135. ground plane should be good, no ground loops, PCB only glass epoxy and low leakage caps to be used, then reading will be stable, use some coating on soldered PCB.
  • An electrically Noisy environment can be simulated with a hair drier, or hot air blower. Another way Looping the NC (normally closed) contacts of a 230V Electrical Contacter-Relay can make it oscillate, this makes a lot of Sound and more important is the Electrical noise rich in EMI-RFI. This helps basic testing of timers, counters, uP, uC and embedded systems as they may malfunction in noisy environment.
  • A Single Pole 12V 100mA relay in a feedback loop, with its contacts, can make a Electrical or Electromechanical Oscillator. This can test your ground loops and digital circuit decoupling caps. It simulates power spikes which may reset some counters.
  • When a Machine with many stages or even an entire production line has to be automated, a PLC system is easiest to configure. It has digital inputs for limit switches and proximity sensors, it has analog inputs for any other parameter sensor. The PLC output modules can drive Electrical Contactor circuits with 230V Signal or 4-20 mA for an AC drive. The tacho-generator voltage feedback or pulses feedback from a motor can be fed to PLC inputs too.
  • Automation is used to enhance the quality and quantity of the product, also where there is danger to operators or workers. This moves the worker up, into the maintenance and management of materials, machines and systems.
  • Industrial Automation is essential to enhance the manufacturing worker to deliver consistent, repeatable and timely delivery of products. Absence of automation makes quality and deliveries unpredictable and stresses worker on monotonous jobs. When the worker is creatively employed with his machine on automation, it is the best scenario.

Anantha Narayan
Solderman Talks 1702 AD
“Over-Automation is an utopia which is incorrect. This is because if you have no workers in any factory, there are no consumers in that city. No consumers means no sales of goods, no building of houses, no buying of automobiles. All strata of People correctly employed, reasonably paid, seeds consumerism, promotes the economy and markets. Automate everything, economy grinds to an halt.”

Solderman Talks 1702 AD

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