Understanding analog voltmeter calibration

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Discussion Overview

The discussion revolves around the calibration of an analog voltmeter, specifically the Zantum Class 0.5 model. Participants explore issues related to the identification of calibration screws versus wiring terminals, the effects of static electricity on meter readings, and the proper methods for calibration using known voltage sources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion over the function of two screws on the back of the voltmeter, initially believing they were for wiring but later discovering they may be calibration screws.
  • Another suggests using a known voltage source to calibrate the meter and adjusting the screws until the meter reading matches the source.
  • Some participants discuss the identification of the screws, with one questioning whether the screws are indeed calibration screws or terminal connections for wiring.
  • There is mention of a seal indicating that calibration should not be tampered with, leading to uncertainty about the calibration process.
  • One participant describes an issue where adjusting the terminal screws affects the zero reading of the meter, raising questions about whether this behavior is normal.
  • Another participant proposes that mechanical stress from tightening screws might be causing the needle to behave unexpectedly.
  • Static electricity is identified as a potential cause for erratic needle movement, with suggestions for mitigating its effects, including cleaning the meter's front with a finger or using glycol antifreeze.
  • There is a clarification that the blue screws are trimpots used for calibration, contrasting with the green terminal block screws.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact function of the screws or the calibration process, with multiple competing views on whether the screws are for wiring or calibration. The discussion on static electricity and its effects on the meter's readings also reflects differing experiences and interpretations.

Contextual Notes

Participants express uncertainty regarding the calibration process and the effects of static electricity, indicating that further investigation may be needed to fully understand the issues at hand.

  • #31
Upside of 'Analog' is you may see needle twitch. No substitute for well-handled 'scope, but often a ''Huh ??'

Analogue or digital, you must be aware of wave-form, ripple etc etc and how instrumentation responds..

Sadly, this is a big problem with wannabe 'Over Unity' inventors: They embrace inappropriate readings...
FWIW, I was banned from a fun hobbyist electronics site for suggesting their resident 'Over-U' guru dispense with his wondrous array of mismatched instruments and simply attach a festoon of incandescent lights.
Given he was site's major sponsor, I was 'run out of town'...
 
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  • #32
For service work, I use moving coil multimeters in preference to a digital multimeter.

With a DMM, the position of the decimal point is most critical, but is the least visible. Intermittent faults are very hard to find with a DMM. Servicing PWM systems with a DMM is fraught with sampling problems.

For 12V and 24V motor vehicle service, where there are connectors, moisture, dirt, salt, and vibration, a test lamp with a filament will be more honest and produce quicker results, than a high resistance DMM.

A DMM is only needed for setting up power supplies and calibrating instruments.
They are now so much cheaper than a moving coil meter, that DMMs are ubiquitous, and so will lead many beginners into trouble, wasting a lot of time.
 
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  • #33
Baluncore said:
For service work, I use moving coil multimeters in preference to a digital multimeter.

My last couple Fluke DMMs at my last couple EE jobs had bargraph LCD displays in addition to their numeric displays. I usually found them to respond quickly enough to satisfy my need to see quickly changing numbers (well below oscilloscope needs). Have you used any DMM bargraphs like those?
 
  • #34
berkeman said:
Have you used any DMM bargraphs like those?
Yes, but the lower-cost non-fluke meters have slower bar-graphs, while unattended Fluke meters tend to go missing.

Bar-graphs also do silly things while range-switching induced by on-off intermittent signals. There are workarounds, but I am more interested in solving the problem than solving the test instruments.

It's horses for courses, I have low-cost versions of both types of meter at each workbench, and in each vehicle toolbox.

Everything is a compromise. If I need precision, I will use a reference grade meter, but it will not remain lying around, or being shaken in a vehicle.

I do appreciate the John Fluke Manufacturing company differential voltmeters, but I originally learned to read an AVO-8, so I guess moving coils are just an extension of my personality.
 
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