7B21

Rev. 0 | Page 2 of 8

GENERAL 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 VDC 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.

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 (<1Ω) signal is available at the output to

drive loads to 2 kΩ minimum.

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Figure 2