Datasheet AD210 (Analog Devices) - 9

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