Instruction Manual

245364-V May 2002

Model 755A

voltage regulator, providing regulated outputs of +15V and -15V.

Detector Temperature Control

This circuit maintains the detector at a controlled temperature of 150°F (66°C). Temperature is sensed by RT1, a resistance element permanently attached to the detector assembly.

The signal from the sensors is applied to amplifier U6, which drives transistors Q2 and Q3, thus controlling application of DC power from fullwave rectifier bridge CR6 to the two heaters within the detector/magnet assembly; HR1, mounted on the top of the magnet, and HR2, mounted permanently on the rear of the detector assembly.

Case Temperature Control

This circuit maintains the interior of the analyzer case at a controlled temperature of 140°F (60°C). Temperature is sensed by a thermistor on the Control Board adjacent to critical electronic components.

The circuit provides on-off control of heater element HR3 via TRIAC Q7. Heater HR3 is located in the heater/fan assembly.

d.Isolated Current Output Board (Optional)

An isolated current output is obtainable by insertion of an optional plug-in circuit board into receptacle J1 on the Control Board assembly (See Figure 1-2 on page 1-3). The current outputs available by this board are 0 to 20 mA or 4 to 20 mA.

e.Alarm Option

The alarm option provides two sets of relay contacts for actuation of (customer- supplied) alarm and/or process control device(s). The alarm relay assembly has two single-pole, double-throw relays, one each for the ALARM 1 and ALARM 2 contacts. Alarm output connections are on the terminal board shown in Figure 2-1 on page 2-2.

4-8

Theory

Rosemount Analytical Inc. A Division of Emerson Process Management