7B35

Rev. 0 | Page 2 of 8

GENERAL DESCRIPTION

The 7B35 is a single-channel signal conditioning current input

module that interfaces with two-wire transmitters, providing an

isolated protected precision output of either +1 V to +5 V or +2

V to +10 V. Model 7B35 features an isolated 24 VDC loop power

supply for driving the transmitter. 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 105 dB @ 50/60 Hz is provided. Rated to

operate with a nominal +24 VDC supply, Model 7B35 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 two input pins of Model 7B35 are each fully protected up to

120 V rms. The current input signal is converted to a voltage,

then filtered by a one-pole 100 Hz filter. 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 isolated transmitter loop

power supply is unregulated and will provide a voltage that is

proportional to the voltage used to power the 7B35 module. The

isolated voltage provided by the 7B35 is between 13 VDC and

34 VDC for loop currents between 4 mA and 20 mA and supply

voltages between 20.4 VDC and 26.4 VDC. The output section

contains a two-pole low-pass filter (-3 dB @ 100 Hz), a buffer

amplifier and 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 down to

2kΩ.

Figure 2