Voltage measurement

I was measuring 2 voltages today an a train air system. The system is a pressure transducer which takes in 24v supply and outputs a respective voltage dependant on pressure. Only 2 wires in circuit I referenced my voltage reading to earth, battery return and the negative supply from the control unit of the transducer but every time I connected the probes the voltage decreased exponentially to 0v in say 30seconds. Why?

by Tammikplm
July 11, 2022

It seems that your voltmeter provides an unexpected path (in the mega-ohm range resistor) which perturbate the working of the circuit (discharge of a polarized capacitor used to bias an AC signal, as example).

In general, the OUTPUT of the transducer is identified and measured in relation to its own GROUND, also identified, but this can be dependent of the circuit. If not identified, you are on your own, I am afraid, since the amplification can be through an OpAmp, or even with a single BJT, you have three possible configurations!

It is also possible that the transducer communicates the pressure through a protocol, and not with an analogical voltage. In such case, you have to use the equivalent decoder, not a voltmeter. It can even be a wireless protocol!

by vanderghast
July 12, 2022

Thanks for replying. Was thinking capacitor as acts like discharging a pure capacitive circuut . I'll put the schematic on tomorrow but there no Information about how the sensor detects pressure. Funnily enough the one i had a fault on the voltage measurement acted as expected when there was a fault on it as in a supply voltage of 24v that was readable and a return voltage again readable. No system negative on return from the sensor. Just a feed and signal

by Tammikplm
July 12, 2022

No Answers

No answers yet. Contribute your answer below!

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.