AC1059 Datasheet, PDF (8/8 Pages) Analog Devices – Precision, Wide Bandwidth 3-Port Isolation Amplifier

AD210
CHANNEL 1
CHANNEL 2
CHANNEL 3
CHANNEL 4
10T
8.25k
R_G 1kΩ
200kΩ
16
17
19
4-20mA
AD590
R_O ^10T
1kΩ
–V_ISS
AD580
9.31k
+V_ISS
25Ω
18
50k
R_O
14
1kΩ
50k
15
10T _RF
15.8k
16
R_G 5k
17
19
18
50k
14
OFFSET
50k
15
100Ω 10T
+V_ISS
–V_ISS
+V_ISS
–V_ISS
16
39k
+V_ISS
AD OP-07
17
19
E_IN
1.0µF
0.47µF ^–VISS
18
14 +V_ISS
50Ω
50kΩ
15 –V_ISS
+V_ISS
+10V
AD584
20k
20k
+V_ISS
A2
–V_ISS
+V_{ISS 20k}
20k
1M
1k
A1
–V_ISS
A1 A2 = AD547
16
17
19
18
14 +V_ISS
15 –V_ISS
AD210
1
2
30 29
+V_OSS 3
–V_{OSS 4}
AD210
1
2
30 29
+V_OSS 3
–V_{OSS 4}
AD210
1
2
30 29
+V_OSS 3
–V_{OSS 4}
AD210
1
2
30 29
+V_OSS 3
–V_{OSS 4}
+V –V COM
AD7502
MULTIPLEXER _{TO A/D}
CHANNEL
SELECT
COM _{DC POWER}
+15V SOURCE
Figure 22. Multichannel Data Acquisition Front-End
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 output.
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