Center Zero
- Right voltmeter: Taut-band instrument driven by amplifier. 9
voltmeter ranges from 1 mV to 10 V and selectable input resistances from 1 to 200 MOhm.
- Left voltmeter: Taut-band instrument driven by amplifier. 9
voltmeter ranges from 1 mV to 50 V; 8 milliammeter / ammeter ranges 1 mA to 10 A (20 mV drop
shunts). Built-in IR drop contact checking circuit.
Voltmeters with
Amplifiers
- Right voltmeter: Selectable input resistances of 1, 10, 25,
50,100 & 200 MOhm on ranges from 10 mV through 10 V. 1 and 5 mV ranges have fixed
resistance of 1000 Ohms.
- Left voltmeter: 10 MOhm input resistance on all ranges from
10 mV through 50 V. l and 5 mV ranges have fixed resistance of 1000 Ohms.
- Solid State integrated-circuit amplifier.
- Operated by easy-to-replace penlite cells with long
shelf-life.
- Temperature compensated.
- Operating range 0oF to 150oF.
- Short warm-up time.
- Good response time on all ranges.
- Very stable zero. No need to readjust zero when changing
ranges (except for 1 and 5 mV ranges).
- AC filters rejects 60 Hz power system potentials up to 35
VAC.
Selectable
Input Resistance
Right voltmeter: Input resistances of
1,10, 25, 50,100 & 200 MOhms selectable by rotary switch. Selectable input resistance
permits detection of high resistance in the external circuit and the elimination of
resulting errors in nearly all cases. A very important factor in structure to earth
potentials, where errors in reading can be very costly. Note: Does not function on the 1
and 5 mV ranges, which have a fixed resistance of 1000 Ohms.
Overload
Protection
Advanced design features virtually eliminate the chance of
damage to either meter from electrical overload on all volt and millivolt ranges, even the
1 mV range. Tests indicate that the M-3-A2 will withstand AC or DC voltages far in excess
of any encountered in normal field testing. Note that the ammeter shunts are not protected
by the amplifier, and are therefore subject to damage by current overloads.
Instruments
The instruments are special taut-band, high-torque type
built to rigid MC Miller Co. specifications. The instruments are inherently more resistant
to mechanical damage, and since both instruments are identical, one spare instrument can
be used as a replacement for the other. Replacement instruments, if ever needed, are low
in cost and readily available. Scales have clearly marked 110 divisions from end to end
(0.5 V to 0 to 0.5 V and l.l V to 0 to 1.1 V). They are 4.0" long and are of the
mirror type. Pointers are knife-edge type. Full scale and tracking accuracy is within 1
1/2% of full scale except for the 1 and 5 mV.
Shunts
Built-in multi-range ammeter shunt has high overload
capacity and a high degree of accuracy. Use of optional accessory external shunt extends
the range of current measurements to 100 A and can be used with either meter.
Contact Checking Circuit
A built-in I-R drop contact checking circuit is used to
determine when good low-resistance contacts are obtained. Circuit may also be used like an
ohmmeter for checking continuity of test leads.
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