Elenco Electronics M-1007K, Assembly And Instruction Manual

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DC VOLTAGE MEASUREMENT

Figure 4 shows a simplified diagram of the DC voltage
measurement function. The input voltage divider resistors
add up to 1 megaohm. Each step down divides the voltage
by a factor of ten. The divider output must be within the
range –0.199 to +0.199 volts or the overload indicator will
function. The overload indication consists of a 1 in the most
significant digit and blanks in the remaining digits.

AC VOLTAGE MEASUREMENT

Figure 5 shows a simplified diagram of the AC voltage
measurement function. The AC voltage is first rectified and
passed through a low pass filter to smooth out the
waveform. A scaler reduces the voltage to the DC value
required to give the correct RMS reading.

CURRENT MEASUREMENT

Figure 6 shows a simplified diagram of the current
measurement function. Internal shunt resistors convert the
current to between –0.199 to +0.199 volts which is then
processed in the 7106 IC to light the appropriate LCD
segments. When current in the range of 10A is to be read,
it is fed to the 10A input and does not pass through the
selector switch.

Figure 4

Simplified DC Voltage Measurement Diagram

7106

100mV

REF

Low Pass

Filter

200mV

2V

1000V

200V

20V

900k

Ω

90k

Ω

100

Ω

900

Ω

9k

Ω

Volts

Common

Figure 5

Simplified AC Voltage Measurement Diagram

Volts

Common

7106

100mV

REF

Low Pass

Filter

Rectifier

Low Pass

Filter - Scaler

750V

200V

100

Ω

900

Ω

Figure 6

Simplified DC Amps Measurement Diagram

Common

10A

A

9

Ω

.99

Ω

.01

Ω

20mA

2mA

200

μ

A

200mA

10A

900

Ω

100

Ω

2mA

200

μ

A

20mA

200mA

10A

7106

100mV

REF

Low Pass

Filter