Measurement Computing DataShuttle - Manual (Page 62)

6-6 Introduction to Terminal Panels 11-09--01 DataShuttle and DynaRes
Analog Auxiliary Component Area on Terminal Panel
Examples
Example 1: Current sense resistor
The analog boards and terminal panels can measure currents up to 50mA directly. On the Analog
Connection boards and T71 terminal panels there is a 25
Ω precision resistor on the unit itself; dip switches
allow users to selecting between voltage and current input. To measure current on any other type of board,
however, it is necessary to install 25
Ω precision resistor on the terminal panel. This connection for current
measurement is shown below. (To see how this connection adds to the circuit, refer to Figure 10(a).)
Figure 16. Current Measurement Connection
R3 is used as a shunt resistor across the positive and negative lines of the channel in use. To install this
resistor, push the resistor ends through the holes for R3 (from the terminal side) until the resistor lies flat
with the panel surface. On the backside, solder the wires to the holes, and then clip off the extra wire with
pliers. This connection does not require any additional traces to be cut. Be sure to select current
measurement in the software package that you are using.
This installation allows the measurement of voltage across the resistor and the conversion of this
measurement to current using the equation V=IR. Observe the power rating of the resistor you install at R3.
Space is provided for a 1/4 Watt resistor.