10
**Responds to the average value of an AC current, and is calibrated to indicate
the RMS value of a pure sine wave.
***Per ANSI C39.5 April 1974: “The maximum voltage, with respect to Ground,
which may safely and continuously be applied to the circuit of an Instrument.”
1.9
Definition of Accuracy
The voltage and current accuracy of this Instrument is commonly expressed as a
percent of full scale. This should not be confused with accuracy of reading (indi-
cation). For example, +2% of full scale on the 10 volt range allows an error of
±0.20V at any point on the dial. This means that at full scale, the accuracy of
reading would be ±2%, but at half scale it would be ±4%. Therefore, it is advan-
tageous to select a range which gives an indication as near as possible to full
scale.
1.10 Safety Considerations
This Operator’s Manual contains special caution and warning symbols which
alert the user to hazardous operating and servicing conditions. These symbols
appear throughout this publication, where applicable, and are defined on the
inside front cover of this manual under NOTES AND SAFETY INFORMATION.
These instructions must be adhered to in order to ensure the safety of operating
and servicing personnel and to retain the operating conditions of the Instrument.
Table 1-2. Items and Accessories Furnished with this Instrument
Quantity
Description
Number
1
Test Lead Set, one red and one
black (48” long) each with combination
probe tip and removable rubber-sleeved
alligator clip.
00043
*1
1.5 volt, D cell, NEDA 13 F
*1
9.0 volt Cell, NEDA 1604
2
1 Amp, 250 V Fuse, Littlefuse Type #312001
1
2 Amp Fuse, 600 V (Bussman Type BBS or
Littlefuse Type BLS)
1
Operator’s Manual
6-111642
*Batteries are standard items replaceable from local retail stores.
Table 1-3. Additional Accessories
Description
Catalog Number
Deluxe Case
00812
Leatherette Ever-Redy Hard Case, Drop Front
00805
Low-Power Ohm Probe
00414
Model 150-2 Amp-Clamp
00545
23
4.17 Zero Ohms Adjustment
When resistance is measured, the INTERNAL batteries B1 and B2 furnish power
for the circuit. Since batteries are subject to variation in voltage and internal
resistance the Instrument must be adjusted to zero before measuring a resis-
tance, as follows:
a.
Turn range switch to desired ohms range.
b.
Plug the black test lead into the - COMMON jack and the red test lead into the
+ jack.
c.
Connect ends of test leads together to short the VOM resistance circuit.
d.
Rotate the ZERO OHMS control until pointer indicates zero ohms. If pointer
cannot be adjusted to zero, one or both of the batteries must be replaced.
(For battery replacement refer to Section 5.)
e.
Disconnect shorted ends of test leads.
4.18 Measuring Resistance
Voltage applied to a resistance range will cause reading errors if low and dam-
age the Instrument if high. When making in-circuit measurements, make certain
that the circuit is completely de-energized before making connections to it.
When making in-circuit measurements, circuit paths in parallel with the resis-
tance being measured may cause reading errors. Check circuit diagrams for the
presence of such components before assuming that the reading obtained is
correct.
a.
Before measuring resistance in the
circuit make sure the power is off in
the circuit being tested and all capaci-
tors discharged.
b.
Disconnect the shunted component
from the circuit before measuring its
resistance. Then set the range switch
to one of the resistance range posi-
tions as follows (Figure 4-8):
1.
Use R x 1 for resistance read-
ings from 0 to 200
⍀
.
2.
Use R x 100 for resistance read-
ings from 200 to 20,000
⍀
.
3.
Use R x 10,000 for resistance
readings above 20,000
⍀
.
c.
Set the function switch at either - DC
or + DC position. Operation is the
same in either position except if semi-
conductors are in the circuit. (See
paragraph 4.19) Adjust ZERO
OHMS control for each resistance
range.
d.
Observe the reading on the OHMS
scale at the top of the dial.
-D.C.
+D.C.
WARNING
READ MANUAL BEFORE USE
COMMON
ALL TERMINALS 1KV. MAX
270
RX1
RX100
RX10,000
Figure 4-8. Jacks and Switch
Positions for Measuring
Resistance
Содержание 270 Series 5
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