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10
Barrel Temperature Control Module
Wiring Guidelines
Follow these guidelines when planning your system wiring.
• To limit the pickup of electrical noise, keep thermocouple and millivolt signal wires
away from power and load lines.
• For high immunity to electrical noise, use Alpha 5121 (shielded, twisted pair) or
equivalent wire for millivolt sensors; or use shielded, twisted pair thermocouple
extension lead wire specified by the thermocouple manufacturer. Using the incorrect
type of thermocouple extension wire or not following the correct polarity may cause
invalid readings. See IEEE Std. 518, Section 6.4.2.7 or contact your sensor
manufacturer for additional details.
• When trimming cable leads, minimize the length of unshielded wires.
• Ground the shield drain wire at only one end of the cable. The preferred location is at
the I/O chassis ground.
• For maximum noise reduction, use 3/8 inch braid wire to connect cable shields to the
nearest I/O chassis mounting bolt. Then connect the I/O chassis to earth ground.
These connections are a requirement regardless of cable type.
• Tighten terminal screws to 6-8 inch-pounds. Excessive tightening can strip the screw.
• The open–circuit detector generates approximately 20 nano–amperes into the
thermocouple cable. A total lead resistance of 25 ohms (12.5 one–way) will produce
0.5 mV of error.
• Follow system grounding and wiring guidelines found in your SLC 500 Modular
Hardware Style User Manual, publication 1747–UM011.
Publication 1746-IN020B-EN-P - July 2002
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