Precision Control Systems 930 - Manual (Page 16)

Model 930 ControlIR TM Instruction Manual Operating Instructions
Research, Inc. Page 12 of 25
TEMPERATURE
CONTROL OPTION
Setup Summary
Table 4-1 Temperature
Controller
Configuration
THEORY OF
OPERATION
Principles of SCR Power
Control
Figure 4-2 Conduction of one
SCR when turned on
at the beginning of a
half-cycle
This section contains temperature controller configuration information for your system.
Refer to the Model XT19 installation and instruction manual for operating the
temperature controller.
Table 4-1 displays factory configurations made for your system:
Sensor Input (TCT option) ‘K’ type thermocouple scaled 0-2500
°F
Sensor Input (TCP option) 4-20mA signal scaled 0-2500
°F
Control Type: PID (proportional, integral & derivative)
AL 1 (alarm 1): Full scale high, non-latching, set for 2000
°F
(This alarm will trip a relay connected to TB100 pins 13
and 14)
Control Output: 0-20 milliamps
This alarm may be re-configured as necessary for your process
SCR type power controllers control power by regulating when silicon controlled
rectifiers (SCRs) conduct AC line current to the load.
A SCR is a solid-state, electronic switching device that turns on (fires) very quickly
when a low-level “gating” signal is applied to its gate electrode. The timing of the
gating signal, and therefore the length of time the SCR conducts, is determined by the
controller’s firing circuitry in response to a control signal. The greater the percentage
of time the SCR is on, the greater the average power it allows to pass through to the
load.
The Model 910 uses a random-fire solid state relay within its SCR poser controller.
This relay is a package consisting of 2 SCRs and a gate drive circuit.
During the positive half-cycle of the AC line voltage the SCR’s anode is positive with
respect to its cathode, so during that half-cycle the SCR will begin to conduct
whenever a gating signal is applied to its gate electrode (see figure 4-2). Once turned
on, an SCR will continue to conduct until its anode-to-cathode voltage drops to zero, so
the SCR continues to conduct until the end of the half-cycle.
INPUT LINE VOLTAGE
FIRING
CIRCUITRY CONTROL SIGNAL
GATING SIGNAL
OUTPUT LINE VOLTAGE
GATE
CATHODE ANODE