Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 62)

Publication 900-UM007D-EN-E - January 2011
2-24 Preparations
• Always connect an AC load to a Triac (AC) relay output. The output will
not turn OFF if a DC load is connected.
• A voltage output (control output) is not electrically isolated from the
internal circuits. Therefore, when using a grounded thermocouple, do
not connect any of the control output terminals to earth ground. If
control output terminals are connected to ground, errors will occur in
the measured temperature values as a result of ground loop leakage
current. With 900-TC8, however, voltage output (Control Output 2) is
functionally isolated from the internal circuits.
• Control Output 2 of the 900-TC16 is a voltage output (SSR driver) only,
and outputs across terminals 11(+) and 12(-), or 14(+) and 15(-).
• Control outputs 1 and 2 (voltage outputs) are not isolated.
• 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 (LBA) and Heater Short Alarm (HSA) that are
provided for the Bulletin 900.)
Figure 2.22
Table 2.I — 900-TC16
Output Type Output 2 Specifications
Voltage (PNP) PNP type, 12V DC
±15%, 21 mA (with short-circuit protection)
1
2
Triac (AC)
relay output Varistor
Varistor
Inductive
load