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M102E/M501 TRS THEORY OF OPERATION
(Addendum to M101E Manual - P/N 04740 Rev A)
9.4.2. M501-TRS electronics
Electronically the M501-TRS is a simple device. The nucleus of the instrument is a programmable,
P-I-D temperature controller which manages the temperature of the instruments’ AC powered
converter oven based on analog input from K-type thermocouple attached to the converters
chamber.
HEATER
AC Heater
Control Relay
Quartz Converter Tube
K Thermocouple
P-I-D
CONTROLLER
SPST ALARM
Thermal
Switch
Alarm Output
Connector
M501-TRS
Figure 9-4: M501-TRS Electronic Block Diagram
The P-I-D controller determines the differences between the actual temperature of the oven
(called the process value or PV), compares it to the target temperature (called the set point or
SV) and changes the percentage of time the heater is turned on versus the time it is turned off
accordingly. The higher the proportion of ON-time versus OFF-time the faster the oven is heated.
For instance, if the PV is much lower than the SV the P-I-D will keep the heater turned on 100%
of the time resulting in a relatively rapid increase in the temperature of the oven. As the PV
approaches the same temperature as the SV the ON cycles get shorter compared to the OFF
cycles.
The M501-TRS’s P-I-D controller includes sophisticated software that allows the controller to track
the rate change in temperature of the oven compared to the percentage of heater ON-time and
predict the proportion needed to reach and maintain the proper oven temperature with a minimal
amount of overshoot or fluctuation.
9.4.2.1. Thermal Switch
While the M501-TRS’s P-I-D Controller includes many safeguards that prevent runaway heating of
the converter oven, as an additional safety backup the M501-TRS includes a heat sensitive switch
which automatically interrupts power to the heater if before the oven temperature reaches critical
levels.
05514 Rev A1 49