How does a multimeter work?

Answer 1

You place the leads across the part of the circuit you wish to evaluate and look at the display. Choosing the right range on the meter will improve accuracy. Make sure there is no power applied to the circuit!

Answer 2

Modern multimeters are digital transistorized volt meters (DTVM) with one or more switches and various sockets to plug the probes into to permit a wide variety of different measurements to be made (e.g. voltage, resistance, current, capacitance, inductance). Some fancy multimeters also provide means for other measurements (e.g. frequency, transistor testing, miniature oscilloscope).

The transistorized input stage of the DTVM has an input impedance of at least 10 megohms to minimize the effects on the circuit being measured. This drives a dual-slope-integrator analog stage that performs the actual measurement under control of a digital timer/counter stage. To perform each measurement the digital timer/counter stage is initialized to run for a constant time period and the dual-slope-integrator analog stage begins integrating the input signal. When the digital timer/counter stage reaches zero it switches to counter mode and the dual-slope-integrator analog stage begins integrating a constant voltage of opposite polarity to the dual-slope-integrator analog stage output voltage at that time. When the output of the dual-slope-integrator analog stage crosses zero the digital timer/counter stage is stopped and the measurement is complete. The value in the digital timer/counter stage is sent to the display stage. This system of measurement minimizes the effects of the various sources of analog errors.

• For voltage measurements of different scales the timer constant and/or the constant voltage is scaled and the value shown on the display is scaled back.
• For resistance measurements a current source is switched in across the transistorized input stage and the DTVM measures the resulting voltage across the resistor. Scaling can be handled in the current source and/or as is done for voltage measurements.
• For current measurements a low value resistor network is switched in across the transistorized input stage and the DTVM measures the resulting voltage across the resistor network. Scaling can be handled in the low value resistor network and/or as is done for voltage measurements.
• etc.

Answer 3

All calibration is about is comparing some reference measurement (derived from a standard instrument) to an unknown measurement which is the measurement indicated by the unit under test (UUT). If we take the above principle into account then calibration of the multimeter is simply about obtaining a reference power supply (this power supply should be traceable to interational standardization bodies such as NIST, A2LA or UKAS etc. as indicated by its calibration certificate). The readings indicated by the power supply are assumed to be "true" or accurate and the multimeter readings are compared to these. Calculation of uncertainties in measurements can be calculated using UKAS' M3003 or the ISO Guide for Evaluating Uncertainties in Measurements. Hope this helps, miguelandrews@gmail.com

Answer 4

Meters of this type today have either an analog or a digital display, but this distinction does not affect their operating principle.

I'll consider the analog type in the discussion.

Central to their operation is an electrical meter; that is a small electromagnetic coil which carries the test current, sitting between the poles of a permanent magnet. This operates against the restoring force of (generally two) spiral hairsprings.

The current in the coil makes the coil move, and thus indicate the electric current.

But may be calibrated as for Volts, Ohms, or Amperes; or multiples and sub-multiples of these.

For volts, a resistor is wired in series with the coil. Thus a series of different resistors, switched into the circuit as needed, will allow a wide range of voltages to be measured.

Exactly similar for current, except in this case, the resistors (commonly called shunts) are wired in parallelwith the coil. Thus de-sensitising the coil operation.

For ohms, there is no external source of electric power available, and that is supplied by a dry cell, or a battery of them, inside the instrument case.

Once again, a series of resistors allows the value of the indicated ohms to be changed.

For Digital meters, an electronic version of the current coil is substituted. Usually as a voltmeter.

Answer 5

Put it in amps or milliamps mode, switch the leads to the correct jacks if necessary, most meters with a high amps scale use different jacks, and put the meter in series with the circuit to be measured. Unless you know for sure what the result should be, start with the highest scale.

Answer 6

You can measure the current on any part of your circuit with a multimeter by first selecting the correct multimeter setting for measuring the current you want, then you have to open the circuit on the part you want to measure, finally use the multimeter in ampmeter mode to complete the circuit. The reason you can't measure current in parallel in a multimeter is because the multimeter uses an internal resistance which is often large in comparison to most circuits, which means that current would not flow or flow more "slowly" than what the flow of current really is through the multimeter. Therefore to measure current you always do it in a series connection.

Answer 7

mainly 3 measurement, 1st Voltage, 2nd, Current, 3rd, resistance

Answer 8

A typical multimeter can be used to measure voltage, current, and resistance

Answer 9

yes i usualy set the multimeter to the highest resistance range by turning the dial to the highest "ohm" setting.