Parr Instrument 4848B - Manual (Page 18)

4848B Reactor Controller
P a r r I n s t r u m e n t C o m p a n y 16
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 Parr 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 4848B Parr Controller, always specify the reactor
with which it will be used so that a thermocouple of
the proper style and length can be furnished.
Motor Speed Control
Parr 4848B Controllers are equipped with a solid
state speed control module for use with the variable
speed, DC motors installed on Parr stirred reactors.
The module itself (approximately 4 inches square) is
mounted inside the chassis on the bottom plate. A
motor switch and a speed adjustment potentiometer
are mounted on the front panel. Each module also
requires a resistor matched to the horsepower of
the motor with which it will be used, as listed in the
following table:
Motor
Rating
Motor
Voltage
Resistor
Required
Parr Part
Number
1/17 HP 90 VDC 0.25 ohm 876E6
1/8 HP 90 VDC 0.10 ohm 876E3
1/4 HP 90 VDC 0.05 ohm 876E
1/4 HP 180 VDC 0.10 ohm 876E3
1/2 HP 90 VDC 0.025 ohm 876E2
1/2 HP 180 VDC 0.05 ohm 876E
3/4 HP 180 VDC 0.035 ohm 876E5