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Functional Description
 The 7B21 is a unity
gain single-channel signal conditioning module that interfaces,
filters and isolates a ±10 Volt input signal and provides
a protected precision output of ±10 Volt. Model 7B21 features
a nonlinearity of ±0.02% maximum and an accuracy of ±0.1%
maximum (±0.01% typical). To accurately measure low level
signals in electrically noisy environments, 1500 V rms of
galvanic transformer-based isolation with a common mode
rejection (CMR) of 100 dB @ 50/60 Hz is provided. Rated
to operate with a nominal +24 V DC supply, Model 7B21 is
mix-and-match and hot-swappable with other 7B Series input
modules, so it can be inserted or removed from any socket
in the same backplane without disturbing system power.
Inside the 7B21 Series Module
The floating differential input of Model 7B21 is fully protected
up to 120 V rms line voltage. A one-pole 300 Hz filter preconditions
the input signal prior to a low drift differential input
amplifier. Amplitude modulation is used to implement transformer
isolation (1500 V rms input-to-output and power). Isolated
front-end circuitry power is supplied by a DC/DC converter.
The output section contains a two-pole low pass filter (-3
dB @ 300 Hz), a buffer amplifier and a power oscillator.
The two-pole output filter and subsequent buffer ensures
that a low noise, low impedance (<1  )
signal is available at the output to drive loads to 2 kminimum.
Figure 1. 7B21 Functional Block diagram
| Input
Output
|
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Figure 2. 7B21 Input Field Connections
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7B21 Models Available
| Model |
Input Range |
Output Range |
|
7B21
|
-10 V to +10 V |
-10 V to +10 V |
7B21 Specifications
(typical @ +23℃ ±5℃ and Vs = +24 V
dc)
| Description |
Model 7B21 |
Input Ranges |
| Standard Ranges |
-10 V to +10 V |
| Custom Ranges |
Not Available* |
| Output Range Options (RL
> 2 k) |
-10 V to +10 V |
Accuracy1 |
| Initial @ +25℃ |
±0.01% Span (±0.1% Span, maximum) |
| Nonlinearity2 |
±0.02% Span, maximum |
| Input Offset vs. Temperature |
N/A3 |
| Span vs. Temperature |
±35 ppm/℃ |
| Output Offset vs. Temperature |
±0.001% Span/℃ |
| Input Bias Current |
+3 nA |
Input Resistance |
| Power ON |
2 M |
| Power OFF |
30 k,
minimum |
Output Noise |
| 5 MHz Bandwidth |
6 mV peak |
| 10 Hz to 100 kHz Bandwidth |
1.5 mV rms |
| 0.1 Hz to 10 Hz Bandwidth |
6 µV peak |
| Bandwidth, -3 dB |
300 Hz |
| Output Rise Time, 10% to 90% Span |
1 ms |
Common-Mode Voltage (CMV) |
| Input-to-Output and Power |
1500 V rms continuous |
Common Mode Rejection (CMR) |
| Input-to-Output and Power @ 50/60
Hz |
100 dB |
| Input Protection |
120 V rms, continuous
±35 V dc, continuous |
| Input Transient Protection |
ANSI/IEEE C376.90.1-1989
IEEE-STD 472
IEC 255-4, Class II |
| Output Resistance |
< 1 |
| Voltage Output Protection |
Continuous Short to Ground |
Power Supply |
| Voltage Range, Operating |
+19 V dc to +29 V dc |
| Current |
+35 mA, maximum |
| Sensitivity |
±0.0001%/% of Vs |
| Mechanical dimensions |
1.663" x 2.11" x 0.563"
(42.24 mm x 53.6 mm x 14.3 mm) |
| Weight |
60 grams |
Environmental |
| Temperature Range |
| Operating |
-40℃ to +85℃ |
| Storage |
-40℃ to +85℃ |
| Relative Humidity, 24 hours |
0 to 90% @ +60℃ noncondensing |
| ESD Sensitivity |
IEC 801-2, Level 2 |
| RFI Susceptibility |
±0.5% Span error @ 400 MHz, 5 Watt,
3 ft |
Warm-up time required
to meet specifications is approximately 10 minutes.
* Contact factory for OEM requirements.
1Includes the combined effects of repeatability,
hysteresis, and nonlinearity.
2Nonlinearity is calculated using best-fit
straight line method.
3Rz is the value of the RTD resistance at
the lowest measurement point. Rspan is the
change in resistance over the measurement span.
Specifications subject to change without notice.
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