Operating instructions

University of Saskatchewan
Electrical Engineering Laboratory Equipment Manual
Analog Meters
There are a wide variety of analog meters available in the labs. There are ac &
dc voltmeters, ac & dc ammeters, ac & dc wattmeters, and several true rms voltmeters.
They are all designed to read accurately only when they are lying flat on their back.
You cannot stand these meters up, as the meter movement was not meant to have the
additional burden of gravity acting on the needle. Most of these meters are found in
2C70 and 2C74, although there are some scattered throughout the machines labs
(2C61 & 2C75).
Their identification and operation is straightforward. Ammeters are identified by a
large ―A‖ on their face, while voltmeters have a large ―V‖. Meters intended only for dc
measurements will have a horizontal line next to the ―A‖ or ―V‖ identifier. Meters
intended for ac measurements will have one cycle of a sine wave instead. If a meter
has both a horizontal line and a sine wave, that meter may be used for either ac or dc
operation. If you need information regarding the internal resistance(s) of the meter
you’re using, that information is usually found on the bottom of the meter.
The ammeters or voltmeters usually have multiple connection posts,
corresponding to different full scale currents or voltages. In addition, they have one
post marked‖; treat that as the positive post. In the case of an ammeter, it should be
hooked up such that the current flows into that post, and out of one of the numbered
posts. In the case of a voltmeter, the post should be connected to the higher
potential, while one of the numbered posts should be connected to the lower potential.
Be sure that you are able to read the meter correctlythe different scales on its face
correspond to the different posts. It’s quite easy to misread a meter if you are looking at
the wrong scale.
Some (but not all) ammeters have been retrofitted with internal shorting switches.
Most of these switches have been placed on the left side of the ammeters. The shorting
switches are there to protect the meters in the event that the current actually going
through them is higher than their rating. Always place the switch in the short position
before powering up a circuit, then place it in the measure position once it has been
turned on. If the needle ―pegs‖, turn it back to the short position and turn off the circuit.
Either something is connected wrong to cause the current to be higher than you
anticipated, or you have simply selected a current scale that is too low.
Wattmeters are slightly different from the ammeters and voltmeters, but they’re
still relatively easy to use. Wattmeters have two sets of coils, the current coil (CC), and
the potential coil (PC). The CC is connected just like an ammeter, that is, in series with
the load. The PC is connected just like a voltmeter, that is, in parallel with the load.
Like an ammeter or a voltmeter, each set of coils has its own terminal, and different
voltage and current scales represented by different numbered connection posts. There
are two general ways of connecting a wattmeter, each illustrated on the following page.

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