Sutron Corporation Satlink Operations & Maintenance Manual, Rev 8.04.2 11/3/2016 pg. 80
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 signal ground to establish the voltage on the
network, you are assured of having a positive voltage with respect to signal ground. 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.
9.3.4.4. Input Range
This setting is relevant only to analog differential measurements. Remember that the system
must read a voltage that falls into the common mode range mentioned in the above note.
Voltages that are negative with respect to the SIGNAL GROUND terminal may not be measured.
The following options are available:
-39 to +39mV
-312 to +312mV
-2.5 to +2.5V
-39 to +39mV with Bias
-312 to +312mV with Bias
Note that the ranges for absolute measurements are nominal. Guaranteed analog input
range over temperature is 0-4.98 V, ± 2.49 V, ± 311 mV, and ± 38.9 mV.
Choose the option that is close to and greater than the input range of the sensor that is being
connected.
For example, if a sensor provides a reading from 0 to 100mV, choose the 312mV option. If you
were to choose the 39mV option, when the sensor provided a reading greater than 39mV, the
unit would indicate a sensor failure.
Use the range “with Bias” if the sensor is not powered by Satlink such as a pyranometer or
thermocouple.
9.3.4.5. 4-20 mA
Connection: 4-20ma IN (Terminal #23)
This input is designed to function with sensors that have a 4 to 20ma current loop interface. This
type of interface is superior to voltage outputs when the cables to the sensors must travel a long
distance or when the equipment is located in electrically noisy environments. Satlink will
measure the current flowing when connected to the 4-20ma Input. Typical 4-20ma sensors will
give a 4 to 20ma current for a 0 and 100% FS. Readings that are greater than 21mA will be
considered a fault. The current required for the sensor is provided by the 2 wire loop and does
not typically require additional connections.
NOTE: Satlink does not provide a dedicated power supply for 4-20ma sensors. The sensor shall
have its own supply or run off the 12 volt supply of Satlink. While the internal 4-20 measurement
is made using an accurate 100 ohm resistor, the overall loop resistance is 200 ohms due to an
additional 100 Ohms series protection resistor. This means that a sensor at a full 20 ma current
output, approximately 4 volts should be allotted for overhead voltage. This is typically not an
issue when an external voltage source is provided to operate the sensor that may be in the 18 to
24 volt range. However, if a 12.5 volt battery is used to source the voltage for the sensor in the
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