Parr Instrument 4838 Operating Instructions Manual page 15

If the secondary temperature (PV) exceeds the alarm
setpoint (SV), the alarm indicator on this display will
illuminate and the High Limit breaker will trip, inter-
rupting power to the heater.
The High Temp Cut-Off Alarm setpoint may be ad-
justed by doing the following:
1. Press the up or down arrow until the lower
display shows the desired setpoint. The lower
display will blink, showing the value has not
been set yet.
2. Press the set button. The lower display will stop
blinking, showing the new value has been set.
This secondary temperature module does not con-
trol the heater. It is used as an alarm only.
When ordering this option separately or installed in
the 4838 Controller, always specify the reactor
with which it will be used so that a thermocouple of
the proper style and length can be furnished.
External Heater Temperature Limit Control
Module (ETLM)
TEMPERATURE
ETLM
This module should be considered in systems with
large thermal lags or long dead times such as gas
phase reactions or other systems where tempera-
ture control is diffi cult.
This confi guration is similar to the High Tempera-
ture Cut Off Module (HTM), but the display will now
turn off the heater if it exceeds a pre-set adjustable
setpoint. This non-latching setpoint will establish a
maximum wall temperature, and combined with the
main temperature control module will help suppress
overshoot in diffi cult to control processes.
As an added safety feature, there is also a second-
ary alarm which will trip the High Limit Reset when
breached. This secondary alarm provides a redun-
dant high temperature safety cut-off which will shut
down the reactor heater if an unusual malfunction
should develop in the primary control system. It is
a completely independent safety backup system,
operating in addition to the high limit control built
into each temperature controller. It has its own
thermocouple, digital display and wiring, and can be
preset to shut down the heater at any desired tem-
perature.
To set the primary (non-latching) temperature limit,
press the up or down arrow on the display. The set-
point value on the right will fl ash. Press the set but-
ton to solidify this display and complete the change.
If the heater temperature exceeds the ETLM setpoint
(non-latching), the output to the heater will be inter-
rupted. This will not trip the High Limit Reset, and
when the heater temperature falls back below the
primary setpoint, it will allow power to fl ow to the
heater again.
To set the secondary (latching) temperature limit,
press the circular arrow key three times. The left-
hand display will read ALIH and the right-hand
display will read the secondary temperature limit
setpoint (usually 375 °C). Press the up or down ar-
row on the display. The setpoint value on the right
will fl ash. Press the set button to solidify this dis-
play and complete the change.
When ordering this option separately or installed in
the 4838 Controller, always specify the reactor
with which it will be used so that a thermocouple of
the proper style and length can be furnished.
4838 Reactor Controller
15