Measurement Computing DataShuttle - Manual (Page 63)

DataShuttle and DynaRes 11-12-01 Introduction to Terminal Panels 6-7
Example 2: 3-Wire RTD components
The most popular connection for RTDs is the three wire type. This sensor requires the installation of
resistors R3 and R4 except for these DataShuttle RTD model, where both resistors are already installed
Consult Set Resistor Values on page 5-7 for R3 & R4 values. Both resistors are already installed in the
T71-RTD panels.
Figure 17. 3-Wire RTD Components
However, if you need to install these resistors yourself then do the following: Figure 14 and Figure 15 show
the possible locations of R3 and R4. Figure 11 will show you that R3 and R4 need to be connected as in
Figure 18. R5 is already in place and should not be removed. To install these resistors push the resistor ends
through the holes for R3 and R4 as shown in Figure 14 (from the terminal side) until the resistor lies flat
with the panel surface. If two wires cannot fit into the Vref hole then one wire may be soldered to another
that is already inserted. On the backside, solder the wires to the holes. Then clip off the extra wire with
pliers. The auxiliary component area in question will now look like Figure 18 below. This connection does
not require any additional traces to be cut.
Figure 18. 3-Wire RTD Connection
Example 3: Ground loops
Occasionally there is an installation where the ground connection is made at the sensor, but it is not reliable.
The solution to this “intermittent” ground is to replace the COM to GND(A) jumper wire at R5 (Figure
10(a)) with a 10 MW, 5%, 1/4 Watt resistor. This provides a ground reference for the analog inputs in
question, but allows very little ground current to flow. In very noisy environments with intermittent
grounds, a smaller resistor may be used if the readings are erratic. This connection is shown is Figure 19
below.
Figure 19. Ground Loop Connection