Data Translation DT300 Series, User Manual

Page: 50 / 164

Chapter 4
50
Note that since they measure the difference between the signals at the high (+) and low (
−
)
inputs, differential connections usually cancel any common-mode voltages, leaving only the
signal. However, if you are using a grounded signal source and ground loop problems arise,
connect the differential signals to the STP300 screw terminal panel as shown in
Figure 11 . In
this case, make sure that the low side of the signal (
−
) is connected to ground at the signal
source, not at the STP300 screw terminal panel, and do not tie the two grounds together.
Figure 11: Connecting Differential Voltage Inputs from a Grounded Signal Source
(Shown for Channel 0)
Connecting Current Loop Inputs
Figure 12 shows how to connect a current loop input (channel 0, in this case) to the STP300
screw terminal panel.
Figure 12: Connecting Current Inputs (Shown for Channel 0)
TB18
Grounded
Signal
Source
+
-
TB1
TB2
Analog In 0
Analog In 0
Return
E
s
Signal Source
Ground V
g1
STP300 Panel
Resistor R1 should be installed for bias
return in case the external ground is floating.
R1
Analog Ground
STP300 Panel
TB1
Analog Input 0
Analog Input 0
Return
TB2
TB18
Analog Ground
4 to 20 mA
+V
CC
R1
R9
Use current shunt resistor R9 to convert current to voltage; 250
Ω
for 4 to 20 mA = 1
to 5 V. The common-side of the external loop supply must either connect to analog
ground or, if needed, to a bias return resistor (R1 in this case).