Sutron Corporation X-Link Operations & Maintenance Manual, Rev 1.63 5/24/2016 pg. 83
Reading Negative Output Voltages on Differential Inputs:
In limited cases, sensors with negative outputs may be used on the differential
inputs with the following limitations:
1)
The negative line from the sensor must not connect to the digital ground of
the sensor with the sensor making a ground connection to the ground
(including antenna ground) of the X-Link logger. (i.e. the sensor outputs
must be able to be floated with respect the grounding of the sensor itself)
2)
The negative voltage (or positive voltage) must remain within the range of
the differential input range selected.
3)
The common mode input range of the differential inputs must not be
exceeded.
While the differential inputs are capable of reading negative voltages, it is
important to keep the voltages with respect to ground within in the common
mode input range of 0.5 to 3.7 volts. In the case of a bridge sensor, by using the
vref and agnd to establish the voltage on the network, you are assured of having
a positive voltage with respect to agnd. In the case of the bridge, you simply
need to remain within the voltage range selected (see 6.1.4.12 below) and
simultaneously remaining in the common mode range of the inputs or 0.5 volts
to 3.7 volts.
The diagram below shows how to make such a connection:
