Measurement Computing CIO-DAC02 - Manual (Page 13)

13
Chapter 3
Functional Details
Analog outputs
Each D/A converter has three analog outputs; a unipolar voltage, a bipolar voltage and a 4-20 mA current
output. The range of the output is determined by the reference voltage selected on that D/A's VREF input. The
CIO-DAC02 provides two on-board jumper selectable reference voltages; -5V and -10V.
Choosing a VREF input of -5V provides a range of 0 to +5 volts on the unipolar output and ±5V on the bipolar
output. The 4-20 mA output is also available at this setting.
Choosing a VREF input of -10V provides a unipolar output of 0 to +10 volts and a ±10V bipolar output.
Choosing an external voltage reference will provide:
 A unipolar output equal to: VREF/4096 * (D/A value) * (-1)
 A bipolar output equal to: VREF/2048 * ( (D/A value) -2048 )
4-20 mA outputs
In addition to voltage outputs, each D/A can supply a 4-20 mA output with a resolution of 0.0039 mA per bit.
You can use the 4-20 mA outputs to control devices in a 4-20 mA control loop. The 4-20 mA current loop
circuit is a precision current sink employing a VMOS FET. A diode provides reverse hookup protection (see
Figure 6).
Select the on-board -5V reference for 4-20 mA use (see Figure 4 on page 11).
+
-
UNIPOLAR OUT
4mA
4-20mA OUT
LLGND
4-20mA CURRENT LOOP OUTPUT
Figure 6. 4-20 mA loop output – simplified circuit diagram