Model 755A

Instruction Manual

245364-V May 2002

where

Vo = the corrected output signal

Vx = the amplified detector-output signal, which includes a pressure factor

Vz = the pressure signal derived from: (a) The pressure sensor and associated amplifiers, and (b) the positive reference voltage power supply

k = the constant that is characteristic of the circuit

Amplifier U8

This amplifier works in conjunction with analog divider U6, providing conditioned output signal Vo as described in Pressure Compensation Circuit above.

Amplifier U10

U10 is an non-inverting buffer amplifier that incorporates an anticipation arrangement in its input network, thus providing slightly faster response time (90% of fullscale on the readout device(s).

Potentiometer R30 provides a continuously variable adjustment of 5 to 25 seconds for the electronic anticipation time and is factory-set for 20 seconds.

Since the anticipation network attenuates the signal, a gain of 10 is provided in U10 to restore the signal to the desired fullscale range of 0 to 10 VDC.

The pressure-corrected signal from U10 is routed to two output circuit:

Digital Output Circuit. The signal from U10 passes through TEST switch SW1 and a filter circuit to an integrating analog- to-digital converter. The resulting digital signal drives the liquid crystal display.

Analog Output Circuit . The output from U10 is provided as an input to the recorder output amplifier. This circuitry

provides zero suppression, scale expansion, and amplification preparatory to use for potentiometric recorder, voltage-to-current conversion for current recorder, and/or alarm functions.

Zero suppression is obtained as the sum of (1) a jumper selectable, fixed value of 0%, 20%, 40%, 60%, or 80% and (2) a continuously adjustable value of 0% to 25%.

The scale expansion factor is jumper selectable for 1, 10, or 100.

Potentiometric output is jumper selectable for 0 to 10mV, 0 to 100mV, 0 to 1V, or 0 to 5VDC.

c.Case Board

The Case Board contains power supply and temperature control circuits. The board is mounted inside of the analyzer case (see Figure 1-2 on page 1-3).

The various circuits operate on main power transformer T1. The two primary windings of T1 are configured (at the factory) for operation on either 120 VAC or 220 VAC.

The Case Board consists of the following:

Source Lamp Power Supply

This circuit provides a regulated output of 2.30 VDC to operate incandescent source lamp DS1 within the optical bench assembly. One secondary of main power transformer T1 drives a fullwave rectifier consisting of CR7 and CR8. The output of DS1 is held constant by a voltage regulator circuit utilizing U7, Q4, and Q5.

±15V Power Supply

This circuit provides DC voltages required for various amplifiers and other circuits. Fullwave rectifier bridge CR5 provides both positive and negative outputs. Each is routed through an associated series-type integrated circuit

Rosemount Analytical Inc. A Division of Emerson Process Management

Theory

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