5
1.
INTRODUCTION
1.1
General
The Simpson Model 390-2 Volt-Amp-Wattmeter (hereafter referred to as the Model
390-2 or as the Instrument), has an AC voltmeter, DC voltmeter, AC ammeter and
AC wattmeter all in one compact, convenient instrument.
1.2
Description
This versatile Instrument is extremely rugged and of the highest quality construc-
tion. The full size three-inch meter is of the dynamometer type with a moving coil
armature operating within two field coils. The readings are clearly marked on two
arcs of the scale, one for volts and amperes and one for watts. An unusual and
practical feature is the uniform wattmeter scale of equal divisions which permits
more accurate readings.
A special break-in plug and lead assembly simplifies making connections to
cord-connected devices. The Instrument can also be used with special test leads
when the break-in plug is not used. The panel designations make the connec-
tions for the various ranges apparent. All markings are screened on the panel
with epoxy white enamel for maximum legibility. The ammeter connectors are
identified with a red dot and the voltmeter connectors are identified with a white
dot.
Approximately 2% should be added to the readings. The accuracy of the Model
390-2 is 5% or better of full scale reading. The errors due to phase angle and
frequency are so small that they can be disregarded within the normal frequency
range of 50 to 144 Hz. Approximately 2% should be added to the readings
obtained with 25 Hz current. The current loss in the Model 390-2 is very low and
has no appreciable effect on the readings.
1.3
Technical Data
1.
DC VOLTS:
Ranges:
0-150 and 0-300 volts
Resistance:
Approximately 50 ohms/volt
Accuracy:
5% of full scale
2.
AC VOLTS:
Ranges:
0-150 and 0-300 volts
Resistance:
Approximately 50 ohms/volt
Accuracy:
5% of full scale
3.
AMPERES (AC only):
Ranges:
0-3 and 0-15 amperes
Voltage Drop:
Approximately 0.5 volts
Accuracy:
5% of full scale
4.
WATTS (AC only):
Ranges:
(150 VAC):
0-300 and 0-1500 watts
(300 VAC):
0-600 and 0-3000 watts
Phase Error:
Negligible at 60 Hz, 2% at 25 Hz
Accuracy:
5% of full scale