Elenco Electronics M-1150K, Сборка и инструкция по эксплуатации

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DC Current Measurement
Figure 11 shows a simplified diagram of the DC current measuring circuit. Here the resistors are placed
across the meter to shunt the current. On the 50mA range, the current is fed directly to the meter and the
voltage drop across the meter at full scale deflection is .1 volt. On all of the other ranges, the full scale volt-
age drop across the meter is .25 volts. A .5 amp fuse and special diodes are added to the circuit for pro-
tection against overload.
Figure 11
Resistance Measurement
Figure 12 shows a simplified diagram of the resistance measuring circuit. Here a known 1% resistor, in par-
allel with the meter and the zero adjust resistors, is compared to the external resistor in a series circuit. The
current is supplied by the 3V battery on the X1, X10 and X1K ranges. On the X10K range, a 9V battery is
placed in series with the 3V battery to supply more current to the series circuit. To calibrate the ohms cir-
cuit, the external resistor is made zero ohms by shorting the test leads together. This places the full battery
voltage across the internal resistors. The current in the meter is adjusted to full scale deflection, or zero
reading on the dial. When an external resistor is made equal to the internal resistance, the meter will deflect
to half scale and the dial marking will show its value.
Figure 12
-12-
R12
.96
R9
3K
0.25A / 10A
R10
102
FUSE
--COM
25
2.5
R11
10
50
µ
A
DC 10A
.025
Shunt
D4
D3
R20
18.5
R19
44K
FUSE
-COM
X1
External
Resistor
+
R21
200
R22
34K
X1K
X10
3V
X10K
9V
R25
10K
R24
18K
R23
195K