Ametek SHZF2 SCR Series, Instruction, Operation And Maintenance Manual

Page: 14 / 48

Installation SHZF2/SHZF3 SCR Power Controller
8 Ametek HDR Power Systems Rev 2
3.4 Wiring Overtemperature Contacts
Normally-open (N.O.) heat sink thermostats are standard on all fan-cooled models (rated 90 A and
higher). These thermostats, which close on high heat sink temperature (200 ºF), may be used to
initiate an alarm, shunt trip, or other device for SCR protection. Thermostat connections are on
terminals 23 and 24 as shown in Figure 3.1.
If desired, normally-closed (N.C.) contacts may be substituted for the normally-open (standard). Heat
sink thermostats are optional on units with current ratings lower than 90 amperes and can be ordered
with either N.O. or N.C. contacts
.
FAN POWER
120 Vac
(220 Vac
OPTIONAL)
OVER TEMP
N.O. STANDARD
(N.C. OPTIONAL)
21 22 23 24
Figure 3.1 Fan and Thermostat Connections
3.5 Command Signal Input
HDR’s Zero-Fired SCR Power Controllers have the capability of having either an isolated current or
non-isolated voltage Command Signal input. The standard input impedance is 500 ohms for isolated
and 1500 ohms for non-isolated.
All units are equipped with DIP switches, select “isolated” position for a 4-20 mA command signal and
“non-isolated” for a voltage input such as 0-10 V dc. See Figure 3.2.
The isolated input works best with an offset Command Signal such as 4-20 mA; however, it will work
with both offset and zero based Command Signals. Zero based Command Signals may have a small
amount of non-linearity (input to output) at the low end. This should not be a problem on closed loop
systems.
CAUTION
The application of fan power should precede, or coincide with, the turn-on of
the line voltage source that is to be controlled by the disconnect. How this is
accomplished and ensured is up to the customer.