Spectrum Controls 1769 User Manual page 18

2-4 Compact™ IO Isolated RTD/Resistance Module
User's Manual Pub. 0300241-01 Rev. A
Follow the guidelines below when wiring the module.
General
•
Power and input wiring must be in accordance with Class 1, Division 2 wiring
methods, Article 501-4(b) of the National Electric Code, NFPA 70, and in
accordance with the authority having jurisdiction.
•
Channels are isolated from one another by 500V dc maximum.
•
Route field wiring away from any other wiring and keep it as far as possible
from sources of electrical noise, such as motors, transformers, contactors, and ac
devices. As a general rule, allow at least 15.2 cm (6 in.) of separation for every
120V of power.
•
Routing field wiring in a grounded conduit can reduce electrical noise.
•
If field wiring must cross ac or power cables, ensure that they cross at right
angles.
•
If multiple power supplies are used with analog millivolt inputs, the power
supply commons must be connected.
•
To ensure optimum accuracy, limit overall cable impedance by keeping a cable
as short as possible. Locate the module as close to input devices as the
application permits.
Grounding
•
This product is intended to be mounted to a well-grounded mounting surface
such as a metal panel. Additional grounding connections from the module's
mounting tabs or DIN rail (if used) are not required unless the mounting surface
cannot be grounded.
•
Keep cable shield connections to ground as short as possible.
•
Ground the shield drain wire at one end only. The preferred location is as
follows.
For grounded thermocouples or millivolt sensors, this is at the sensor
o
end.
For insulated/ungrounded thermocouples, this is at the module end.
o
Contact your sensor manufacturer for additional details.
•
Refer to Industrial Automation Wiring and Grounding Guidelines, Allen-
Bradley publication 1770-4.1, for additional information.
RTD Wiring Considerations
•
The module requires three wires to compensate for lead resistance error.
•
If using a 3-wire configuration for module connections, select cable to ensure
that lead wire resistances match as closely as possible. Consider the following:
To ensure temperature or resistance value accuracy, the resistance
o
difference of the cable lead wires must be less than or equal to 0.01 Ω .