Kipp&Zonen AMPBOX Amplifier - Manual (Page 15)

15
3.3 Installing AMPBOX on voltage input
Some data acquisition systems do not have a current input or a voltage input suitable for the low voltage levels of our radiometers.
In such situations an external power supply unit and shunt resistor are required. This power supply will then supply the active
current loop required for the AMPBOX, and the shunt resistor provides the ability to measure the voltage drop over it. Depending
on the resistor value, customized voltage measurements can be achieved suitable for the particular voltage input of the data
acquisition system.
For a 2 to 10 V voltage range a 500 Ω shunt resistor is required (2 V represent 4 mA and 10 V represents 20 mA)
For a 0.4 to 2 V voltage range a 100 Ω shunt resistor is required (0.4 V represent 4 mA and 2 V represents 20 mA)
For a 0.2 to 1 V voltage range a 50 Ω shunt resistor is required (0.2 V represent 4 mA and 1 V represents 20 mA)
The shunt resistor needs to be a precision resistor of 0.05 % and needs to be mounted as close as possible to the data
acquisition system. Preferably directly screwed into the differential inputs, otherwise you will measure the voltage over
the resistor minus the voltage drop of the additional cable which affects the accuracy of your measurement.
Note There is an internal diode that protects the AMPBOX from any damage when the power supply unit is connected
the wrong way around.
Note The power supply should be suitable to supply 7.2 VDC for the AMPBOX + the maximum voltage drop over the shunt
resistor + the voltage drop over the cable loop at 20 mA. The maximum supply voltage at the AMPBOX is 35 VDC.
The voltage drop over the cables can be calculated when the specifications of the cable are known.
Note Install the AMPBOX as close as possible to the radiometer. The cable between the AMPBOX and data acquisition system
can be over 100 meters. It’s therefore advised to install the PSU as close as possible to the data acquisition system.
Example when using adjusted gain setting of 1 mA / 25 W/m² for the pyrgeometer starting at -100 W/m² (CNR 4 downward) and
output is 2000 mV when using a shunt resistor of 100 R.
E = (U
out
- U
offset
) / shunt resisitor * gain setting - E
offset
E = (2000 mV - 400 mV) / 100 * 25 W/m² - 300 W/m²
E = 100 W/m²
Radiometer Ampbox Data Acquisition
DC Power Supply
+ –
voltage input
See Notes
+
+
–
–
shunt
resistor