Teledyne 102E manual 9.4.2. M501-TRS electronics, Thermal Switch, Heater, P-I-D Controller, Rev A1

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

Quartz Converter Tube

K Thermocouple	Thermal
	Switch

P-I-D

CONTROLLER

SPST ALARM

M501-TRS

AC Heater

Control Relay

Alarm Output

Connector

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