Cooper Instruments & Systems DCI 120 Bridge/Strain Gauge Data Loggers - Manual

CF 179 1 Rev A 2008.07.08
DCI 120
20Hz Bridge/Strain Recorder
DCI 120-10
10mV, 20 Hz, Bridge Recorder
DCI 120-25
25mV, 20 Hz, Bridge Recorder
DCI 120-100
100mV, 20 Hz, Bridge Recorder
DCI 120-1000
1000mV, 20 Hz, Bridge Recorder
Configuring the Data Logger
Voltage Divider Configuration
The Voltage Divider configuration is a simple and frequently used setup to measure bridge strain.
1. Jumper between POWER and REF+
2. Place a 12kΩ resistor between REF+ and REF-
3. Jumper between REF- and IN+
4. Place the strain gage between IN+ and IN-
5. Jumper between IN- and GROUND
Conversions
To convert the Voltage values into Ohms, use the following formula:
Example: The software reports a voltage of 20mV in the circuit described above. The strain gage resistance is
therefore:
The resistor Ro between REF+ and REF- and the strain gage value form the mV reference (mVref). This may
be expressed as:
The Bridge120-25 has a resolution of about 2μV. If the resistance of the strain gage changes by +.1, the device
would measure a change of approximately +20μV. Conversely, this voltage resolution translates in Ohms to
approximately:
Note: The maximum voltage must be kept within the specified input range. See data sheet for details.
Product Notes
LEDs
Once started, the LED will flash at the selected reading rate to indicate that the device is running.