AD210
10T
R
G
1kΩ
8.25k
200kΩ
16
17
19
CHANNEL 1
4-20mA
25Ω
50k
1kΩ
18
14
R
O
50k
15
10T
R
F
15.8k
16
R
G
5k
17
19
18
–V
ISS
9.31k
+V
ISS
AD580
50k
100Ω
OFFSET
50k
10T
16
39k
CHANNEL 3
E
IN
1.0µF
0.47µF
–V
ISS
+V
ISS
AD OP-07
17
19
18
14
50Ω
+V
ISS
+10V
AD584
CHANNEL 4
20k
20k
A2
–V
ISS
+V
ISS
A1
–V
ISS
A1; A2 = AD547
20k
20k
1k
1M
15
+V
ISS
50kΩ
15
+V
ISS
–V
ISS
30
29
+V
OSS
–V
OSS
2
14
15
+V
ISS
–V
ISS
30
29
+V
OSS
–V
OSS
3
4
AD7502
MULTIPLEXER
TO A/D
2
+V
ISS
–V
ISS
30
29
+V
OSS
–V
OSS
2
AD210
1
3
4
+V
1
–V COM
AD210
CHANNEL 2
AD590
R
O
1kΩ
10T
AD210
1
3
4
CHANNEL
SELECT
16
17
19
18
14
+V
ISS
–V
ISS
30
AD210
1
2
+V
OSS
–V
OSS
29
3
4
COM
+15V
DC POWER
SOURCE
Figure 22. Multichannel Data Acquisition Front-End
MULTICHANNEL DATA ACQUISITION FRONT-END
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
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.
–8–
REV. A
PRINTED IN U.S.A.
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.
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 output.
C1005–9–9/86
AD [ ANALOG DEVICES ]
