2.3 SIGNAL CONNECTION
Signal connection is important in applying a data acquisition board. In addition to wrong connections, which is the most common
cause of customer calls to tech support, is the possibility of ground loops, floating signal sources and excessive common mode voltage.
Connecting signals to a data acquisition board is not difficult. Please follow the examples shown here and pay close attention to the
grounding shared between the PC and the signal source.
2.3.1 Connector Diagram
The CIO-DAS80# analog connector is a 37 pin D type connector accessible
from the rear of the PC through the expansion backplate (Figure 2-12). The
connector accepts female 37 D type connectors, such as those on the
C73FF-2, 2 foot cable with connectors. The connector pin names Ch# Low
and Ch# High are the differential inputs of the CIO-DAS80#.
If frequent changes to signal connections or signal conditioning are
required, refer to the information on the CIO-TERMINAL and CIO-
MINI37 screw terminal boards. If additional channels or signal condition-
ing is required, refer to the information on the CIO-EXP32, 32 channel
analog multiplexer/amplifier. Isolation amplifiers may be mounted using
the ISO-RACK08 and 5B isolation modules.
2.3.2 Analog Inputs
Analog inputs on the CIO-DAS80# are designed to accept voltage signals
for measurement.
The analog inputs may be configured in three different ways:
1.
True differential inputs. For sources with a separate ground, com-
mon to the PC.
2.
Pseudo-differential inputs used for floating sources has noise rejec-
tion capability
3.
Single ended inputs. Also used for floating sources.
The manner of configuring the analog inputs and the schematic of those
configurations is explained earlier in the manual. This section covers the
implications of a given connection and shows how to make that connection
Figure 2-12. Analog Connector
WARNING - PLEASE READ
TIP: Using a voltmeter, measure the AC and DC voltage between the ground signal at the signal source and the PC.
Place the red probe on the PC ground and the black probe on the signal ground. If there is a difference of more than
10 volts, do not connect the CIO-DAS80# to this signal source because you will not be able to make any reading. If
the difference is more than 30 volts, DO NOT connect this signal to the board because it will damage the board and
possibly the computer. WARNING: Use great care when measuring any voltage. Voltages over 30V can be dan-
gerous to your health.
2.3.3 Single-Ended Inputs
A single ended input is two wires connected to the CIO-DAS80#; a channel high (CH# HI) and a Low Level Ground (LLGND). The
LLGND signal must be the same ground the PC is on. The CH# HI is the signal voltage. Single-ended mode is selected via a switch.
2.3.4 Floating Differential
A floating differential input is two wires from the signal source and a 10K ground reference resistor installed at the CIO-DAS80#
input. The two signals from the signal source are Signal High (CH# High) and Signal Low (CH# Low). The reference resistor is con-
nected between the CIO-DAS80# CH# Low and LLGND pins. This is accomplished with the installation of the SIP resistor pack.
A floating differential hookup is handy when the signal source is floating with respect to ground, such as a battery, 4-20mA transmitter
or if the lead lengths are long or subject to EMI interference. The floating differential input will reject up to 10V of EMI on the signal
wires.
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