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The negative voltage (or positive voltage) must remain within the range of the differential input
range selected.
The common mode input range of the differential inputs must not be exceeded (see below).
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.
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 analog 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 the station. Pyranometer and thermocouple
type sensors should use bias.
4-20 mA
Connection: 4-20ma (Terminal #20)
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. The station 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: The station 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 the station. While the internal 4-20 measurement is made
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