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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 Ω) signal is available at the output to drive loads to 2 kΩ minimum.
Figure 1. 7B21 Functional Block Diagram
Figure 2. 7B21 Input Field Connections
7B21 Models Available
|Model||Input Range||Output Range|
|Order Now||7B21||-10 V to +10 V||-10 V to +10 V|
(typical @ +23°C ±5°C and Vs = +24 V dc)
|Standard Ranges||-10 V to +10 V|
|Custom Ranges||Not Available*|
|Output Range Options (RL > 2 kΩ)||-10 V to +10 V|
|Initial @ +25°C||±0.01% Span (±0.1% Span, maximum)|
|Nonlinearity2||±0.02% Span, maximum|
|Input Offset vs. Temperature||N/A3|
|Span vs. Temperature||±35 ppm/°C|
|Output Offset vs. Temperature||±0.001% Span/°C|
|Input Bias Current||30 pA (200 pA, maximum)|
|Power ON||2 MΩ|
|Power OFF||30 kΩ, minimum|
|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
IEC 255-4, Class II
|Output Resistance||< 1 Ω|
|Voltage Output Protection||Continuous Short to Ground|
|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)
|Operating||-40°C to +85°C|
|Storage||-40°C to +85°C|
|Relative Humidity, 24 hours||0 to 90% @ +60°C 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.
1 Includes the combined effects of repeatability, hysteresis, and nonlinearity.
2 Nonlinearity is calculated using best-fit straight line method.
3 Rz 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.