Datasheet
AD210
REV. A
–8–
MULTICHANNEL DATA ACQUISITION FRONT-END
Illustrated in Figure 22 is a four-channel data acquisition front-
end used to condition and isolate several common input signals
found in various process applications. In this application, each
AD210 will provide complete isolation from input to output as
well as channel to channel. By using an isolator per channel,
maximum protection and rejection of unwanted signals is
obtained. The three-port design allows the AD210 to be
configured as an input or output isolator. In this application the
isolators are configured as input devices with the power port
providing additional protection from possible power source
faults.
Channel 1: The AD210 is used to convert a 4–20 mA current
loop input signal into a 0 V–10 V input. The 25 Ω shunt resistor
converts the 4-20 mA current into a +100 mV to +500 mV signal.
The signal is offset by –100 mV via R
O
to produce a 0 mV to
+400 mV input. This signal is amplified by a gain of 25 to produce
the desired 0 V to +10 V output. With an open circuit, the AD210
will show –2.5 V at the output.
Channel 2: In this channel, the AD210 is used to condition and
isolate a current output temperature transducer, Model AD590. At
+25°C, the AD590 produces a nominal current of 298.2 µA. This
level of current will change at a rate of 1 µA/°C. At –17.8°C (0°F),
the AD590 current will be reduced by 42.8 µA to +255.4 µA. The
AD580 reference circuit provides an equal but opposite current,
resulting in a zero net current flow, producing a 0 V output from
the AD210. At +100°C (+212°F), the AD590 current output will
be 373.2 µA minus the 255.4 µA offsetting current from the
AD580 circuit to yield a +117.8 µA input current. This current is
converted to a voltage via R
F
and R
G
to produce an output of
+2.12 V. Channel 2 will produce an output of +10 mV/°F over a
0°F to +212°F span.
Channel 3: Channel 3 is a low level input channel configured with
a high gain amplifier used to condition millivolt signals. With the
AD210’s input set to unity and the input amplifier set for a gain of
1000, a ±10 mV input will produce a ±10 V at the AD210’s out
put.
Channel 4: Channel 4 illustrates one possible configuration for
conditioning a bridge circuit. The AD584 produces a +10 V
excitation voltage, while A1 inverts the voltage, producing negative
excitation. A2 provides a gain of 1000 V/V to amplify the low level
bridge signal. Additional gain can be obtained by reconfiguration
of the AD210’s input amplifier. ±V
ISS
provides the complete power
for this circuit, eliminating the need for a separate isolated excita-
tion source.
Each channel is individually addressed by the multiplexer’s chan-
nel select. Additional filtering or signal conditioning should follow
the multiplexer, prior to an analog-to-digital conversion stage
.
+V
OSS
+V
ISS
–V
ISS
–V
OSS
AD210
R
O
50k
17
15
18
16
19
14
4
3
29
COM
+V
TO A/D
+V
OSS
+V
ISS
–V
ISS
–V
OSS
OFFSET
50k
17
15
18
16
19
14
4
3
2
30
29
+V
ISS
–V
ISS
15
+V
OSS
–V
OSS
AD210
18
19
14
4
3
2
1
30
+V
OSS
–V
OSS
AD210
17
18
16
19
4
3
1
30
29
R
G
1kΩ
1
200kΩ
8.25k
AD210
1
10T
4-20mA 25Ω
50k
1kΩ
R
G
5k
10T
R
F
15.8k
10T
50k
30
16
17
100Ω
AD590
AD580
–V
ISS
+V
ISS
R
O
1kΩ
10T
9.31k
AD OP-07
+V
ISS
–V
ISS
+V
ISS
–V
ISS
15
14
0.47µF
50kΩ
50Ω
1.0µF
39k
E
IN
1M
1k
20k
20k
20k
20k
+V
ISS
–V
ISS
29
+V
ISS
–V
ISS
A2
A1
AD584
+V
ISS
COM
+15V
DC POWER
SOURCE
2
2
AD7502
MULTIPLEXER
–V
CHANNEL
SELECT
CHANNEL 3
CHANNEL 1
CHANNEL 2
CHANNEL 4
+10V
A1 A2 = AD547
Figure 22. Multichannel Data Acquisition Front-End
C1005–9–9/86
PRINTED IN U.S.A.