Measurement Computing DBK48 - Manual (Page 5)

8B Isolated Signal Conditioning Module 967792 DKB48, pg. 5
Installing Plug-in Resistors to Create 4 to 20 mA Loops with 8B Voltage-Input Modules
WARNING
Electric shock hazard! Turn off power to the DBK48 and all connected modules and
devices before inserting or removing resistors. Failure to do so could lead to injury or
death due to electric shock.
CAUTION
The discharge of static electricity can damage some electronic components.
Semiconductor devices are especially susceptible to ESD damage. You should always
handle components carefully, and you should never touch connector pins or circuit
components unless you are following ESD guidelines in an appropriate ESD
controlled area. Such guidelines include the use of properly grounded mats and wrist
straps, ESD bags and cartons, and related procedures.
Location of Shunt Resistor Plug-In
Shown with shunt resistors plugged-in for Channel 0 (at R0) and Channel 2 (at R2)
Only voltage-input type modules require the plug-in shunt resistors. The plug-in resistors
must be removed for all other module types, including current-input type.
Inputs to monitor the commonly used 4 to 20mA current loops most often employ a 250 Ω precision
resistor to develop a 1 to 5 VDC voltage drop.
Ideally, a resistor for such purpose should have a 0.1% tolerance (or better) with a minimum power rating
of 0.25W and a temperature coefficient of at least 25ppm/°C.
Lower values of resistance, for example, 62.5 Ω [for a lower voltage drop within the loop of 0.25 to 1.25
VDC] will require that the host data acquisition device use a gain of x4 to maximize the signal resolution.
To create a 4 to 20mA current loop :
1. Turn off power to the DBK48 and all connected modules and devices.
2. Disconnect power, all equipment, and signal lines from the DBK48 prior to installing the
resistors. Be aware that isolated measurements can present lethal voltages!
3. Remove the DBK48 top cover plate and set aside.
4. Carefully plug the shunt resistor into the applicable plug-in location for the designated channel;
for example, R0 for Channel 0, R1 for Channel 1, R2 for Channel 2, etc. Repeat for each channel
as applicable.
DO NOT solder the shunt resistors in place.
Only voltage-input type modules require these resistors. The plug-in resistors
must be removed for all other module types, including current-input type.
5. Reinstall the DBK48 top cover plate and secure in place.
Current Shunt
Resistors