Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 60)

Publication 900-UM007D-EN-E - January 2011
2-22 Preparations
Output Wiring Considerations
• Do NOT connect a DC load to the Triac (AC) relay.
• The PNP voltage (SSR) output (Control Output 1) is not electrically
isolated from the controller’s internal circuits. SSR Control Output 2 of
the 900-TC16 is also not isolated. However, SSR Control Output 2 of
the 900-TC8 is isolated. When using a grounded thermocouple, do not
connect any control output terminals to earth ground. If the control
output terminals are connected to earth ground, errors will occur in the
measured temperature values as a result of ground loop leakage current.
• For 900-TC8 & 900-TC16: The 4...20 and 0…20 mA analog output is
electrically isolated from the other controller circuits as follows:
– Analog Output to Sensor Input: 500V AC 50/60 Hz for 1 minute
– Analog Output to Alarm Output: 2000V AC 50/60 Hz for 1 minute
– Analog Output to Input Power Supply: 2000V AC 50/60 Hz for 1
minute
• The life expectancy of the electro-mechanical relay outputs vary greatly
with the switching capacity and other switching conditions. Always use
the output relays within their rated load and electrical life expectancy. If
an output relay is used beyond its life expectancy, its contacts may
become fused or burned.
• Use the Bulletin 900 Controller within the rated load. Not doing so may
cause damage or fire.
• Attach a surge suppressor or noise filter to peripheral devices that
generate noise (in particular, motors, transformers, solenoids, magnetic
coils, or other equipment that have an inductance component).
• About 4 seconds are required for control and/or alarm outputs to turn
ON when the power is initially turned ON to the controller. Take this
into consideration when the temperature controller is incorporated into
a sequence circuit.
• For 900-TC8 & 900-TC16: Triac (AC) relay outputs use
semiconductors for switching when closing and opening the circuit,
thereby eliminating relay chatter and arcing and improving durability
compared to an electro-mechanical relay output. However, if high levels
of electrical noise or surge are imposed between the output terminals,
short-circuit faults may occasionally occur. If the output becomes
permanently shorted, there is the danger of fire due to overheating of
the heater. Design safety into the system, including measures to prevent
excessive temperature rise and fire. Take countermeasures such as
installing a surge absorber. As an additional safety measure, provide
error detection in the control loop. (Use the Loop Burnout Alarm