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CALIBRATION
Batteries
Install the following parts:
1. Install the 9V and the two 1.5V (AA) batteries as shown in Figure 1. Be sure to observe the polarity markings
on the bottom of the battery compartment.
2. Place the thumb wheel knob onto the 0Ω ADJ pot located at the lower right side of the meter dial.
Meter Calibration
(See Operating and Testing the Multimeter Section for meter operating instructions).
1. Before starting tests, set the meter needle to zero . The zero adjust screw is located on the meter face next
to the base of the needle. With no test leads connected, slowly turn this screw until the needle points to zero
on the 0-10 scale immediately below the meter mirror.
2. Obtain a voltage source of 0.4V as measured by an accurate voltmeter. The circuit of Figure 2 will work fine.
3. Set the range switch to 0.5VDC.
4. Connect the test leads as shown in Figure 2.
5. Adjust R8 for a reading of 0.4V (40 on 50 scale) on the M-1250 meter.
If a DC power supply or an accurate voltmeter is not available, then use a fresh 1.5V battery and adjust R6 to
read 1.55V on the 2.5V scale (155 on 250V scale).
Caution: Do not mix alkaline, standard (carbon-zinc), or rechargeable (nickel-cadmium) batteries.
9V Battery
Shunt Wire Calibration
To calibrate the shunt wire, you will need a 5A current
source like a 5V power supply and a 1Ω 25 watt resistor.
If a 5A source is not available, you can use a lower
current (2A). If no supply is available, it is not important
to do this test. Set the range switch to 250A/10A position
and connect the red and black test leads as shown in
Figure 3. Read the current on the 0-10 scale immediately
below the meter mirror. If the meter reads high, resolder
the shunt wire so that there is less wire between the two
mounting holes (move the shunt wire closer to the PC
board). If the meter reads low, resolder the shunt wire so
that there is more wire between the two mounting holes
(move the shunt wire away from the PC board).
1.5V Batteries
Figure 1
-10-
Figure 2
Figure 3
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