Operating instruction for Multimeter


#1

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The combination volt-ohm-milliammeter is a basic tool in any electronic laboratory. The proper use of this instrument increases its accuracy and life. The following precautions should be observed:

1. Start with the highest range of the instrument and move down the range successively, to prevent meter overloading and possible damage when checking voltage or current.

2. For higher accuracy, the range selected should be such that the deflection falls in the upper half on the meter scale.

3. Choose a voltmeter range such that the total voltmeter resistance (ohms per volt x full scale voltage) is at least 100 times the resistance of the circuit under test - For higher accuracy

4. Make all resistance readings in the uncrowded portion on the meter scale, whenever possible.

5. Take extra precautions when checking high voltages and checking current in high voltage circuits.

6. Verify the circuit polarity before making a test, particularly when measuring dc current or voltages.

7. The power to the circuit should be turned off while checking resistance in circuits. Otherwise the voltage across the resistance may damage the meter.

8. Recalibrate the instrument at frequent intervals.

9. Renew ohmmeter batteries frequently to insure accuracy of the resistance scale.

10. Protect the instrument from dust, moisture, fumes and heat.
Also read
Working of Dead Weight Tester


#2

C’mon guys, let’s get with the program.

The photo is a modern day, electronic DVM, a digital mulitmeter.

But the text is from about 1960, when people used Simpson or Tripplet analog/mechanical multimeters.

Several of the points do not apply at all to digital multimeters, DVM’s. Cases-in-point:

  1. “range should be such that the deflection falls in the upper half on the meter scale”

‘Deflection’ refers to a needle moving in an arc above a scale. Where is the needle in the DVM in the photograph? Where is the scale in the DVM in the photograph?

  1. “Choose a voltmeter range . . . . ohms per volt”

Show me the spec for the meter in the photo for “ohms per volt”. You can’t. Analog/mechanical meters had a spec for ohms per volt, but electronic meters use high impedance analog inputs; there is no ‘ohms per volt’ to measure or report as a spec.

  1. “Make all resistance readings in the uncrowded portion of the meter scale”. Show me in the photograph which portion of the scale is crowded and which portion is uncrowded? The photo is only a digital read-out; there is no printed analog indicator plate with a non-linear resistance scale.