Spectrum Controls 1746sc-NI8u - Manual (Page 28)

16 SLC 500 ™ Universal Analog Input Module
transformers, contactors, and ac devices. As a general rule, allow at
least 6 in. (about 15.2 cm) of separation for every 120 V of power.
• Routing the field wiring in a grounded conduit can reduce electrical
noise further.
• If the field wiring must cross ac or power cables, ensure that they cross
at right angles.
• To limit the pickup of electrical noise, keep thermocouple, RTD,
millivolt, and milliamp signal wires as far from power and load
lines as possible.
• For improved immunity to electrical noise, use Belden 8761
(shielded, twisted pair) or equivalent wire for millivolt sensors; or
use shielded, twisted pair thermocouple extension lead wire
specified by the thermocouple or RTD manufacturer. Using the
incorrect type of thermocouple extension wire or not following the
correct polarity may cause invalid readings.
• There is one shield pin for every two input channels. All shields
are internally connected, so any shield terminal can be used with
any channel.
• Ground the shield drain wire at only one end of the cable. The
preferred location is at the shield connections on the terminal
block. (Refer to IEEE Std. 518, Section 6.4.2.7 or contact your
sensor manufacturer for additional details.)
• Keep all unshielded wires as short as possible.
• To limit overall cable impedance, keep input cables as short as
possible. Locate your I/O chassis as near the RTD or
thermocouple sensors as your application will permit.
• Tighten screw terminals with care. Excessive tightening can strip
a screw.
• Follow system grounding and wiring guidelines found in your
SLC 500 Installation and Operation Manual.
Wiring RTD or
Resistance Sensors
to the NI8u Module
The NI8u module supports two, three, and four wire RTDs or
resistance inputs connected individually to the module (channels 4
through 7), as shown in the figure below.