Theory of Operation-OM 501 A
to the Analog Converter
( U 1 601
pi n
15).
In ac current
function. the rnA ac front-panel switch (Sl-l pin
4)
is
closed. The voltage developed across the input current
shunt is coupled to
AC
Bufler
U 1 539.
which is connected
(by Relay
K1528
energizer) as a
X 1 0
gain amplifier. The
voltage at pin
6
of
U 1 539
feed through
R 1 537
to converter
U 1 429
(pin
1)
and outputs at pin 8 of
U1 429.
Through
appropriate switching.
U 1 429
pin
8
oulput voltage couples
to the Analog Converter.
U 1 601
pi n
1 5.
Ac current is also
measured as a true rms ac function.
O hms Converter
0
(Refer to Fig. 3-6)
The ohms converter circuitry generates a known
current that flows out the front-panel VOL TS/o connector
through the unknown resistance. The voltage developed
at the input connectors is proportional to the unknown
resistance. This voltage is sensed by the aid converter and
displayed as an ohms value.
REAR INTERFACE
28B
CONNECTOR
UNKNOWN
RESISTANCE
+5 V
CR1516
1 0 k
The O hms Reference Current Source.
0 1 4 1 5
and
associated circuitry, generates a
100
fJ.A reference
current. This current either flows through R 1 5 1 6 or R 1 5 1 6
i n parallel with t h e series combination of
R1515
and R 1 4 1 2
(lOO) depending on which ohms function and range i s
selected. This reference current develops either
1
V o r
1 0
V across
R 1 5 1 6.
The Ohms Converter
( U 1 5 1 5
and
0 1 525)
applies
1
V or
1 0
V across the attenuator section
selected by the range switches. The attenuatar current,
determined by the range switches. flows through ohms
protection posistor RT1102 and out the VOLTS/O front
panel connector or rear i nterface connector (pin 288)
through the unknown resistance to the LOW front-panel
or rear i nterface connector (pin 28A). The output current
from the VOL TS/O or rear interface connector varies
between
1 00 f.JA
and
1
m A i n decade steps. dependi n g o n
the selected range.
100
90 k
1 k
20 kO
200 Cl
2 kQ
900 k
20 k
200kQ
9 M
2 MCl
o
20 M Q
o
CR1518
U1515
+15 V
01525
34
l
200 Cl
100
IlA
01415
20 MCl
R1516
100 k
R1412
500
R1515
1
0
.
93 k
-12
V
NOTE:
Switches shown In
200 0
position
2749-4A
Fig.
3-6.
Simplified ohms converter diagram.
REV
A JAN
1980
Summary of Contents for DM501A
Page 1: ......
Page 2: ......
Page 6: ...OM 501A OM SOiA Oigita Multlmeter xiv AUG 1980...
Page 13: ......
Page 18: ...Verso Filler Page z z...
Page 21: ...Operating Instructions OM SOlA FIg 2 2 Controls and connectors REV A AUG 1980 English 2 3...
Page 24: ...Verso Filler Page z z...
Page 25: ...OM 501A Japanese 2 3...
Page 26: ...Verso Filler Page z z...
Page 48: ...Verso Filler Page z z...
