Model 755R

Instruction Manual

748213-S April 2002

5-9 ANALOG OUTPUT CIRCUITS FOR RECORDER AND ALARMS

Refer to Figure 5-8, page 5-12. The analog output circuits utilize two amplifiers, first-stage amplifier and second-stage amplifier.

2.Current Output Receptacle J1. This connector accepts the optional plug-in current-output board.

3.Dual Alarm Amplifier Circuit. This cir- cuit drives the optional 654019 Alarm Relay Assembly.

a.First Stage Amplifier

Permits selection of the desired fullscale oxygen range for the recorder via jumper-selectable signal amplification for scale expansion. This amplifier permits selecting the desired fullscale oxygen range for the recorder by an appropriate jumper selection of one of seven recorder spans. The following recorder spans are available: 1, 2.5, 5, 10, 25, 50, and 100%.

b.Second Stage Amplifier

Provides (a) a jumper-selectable output for a potentiometric recorder and (b) an output to drive the voltage-to-current and/or alarm option(s), if used. This am- plifier is an inverting configuration that provides a signal attenuation of 2X, thus reducing the 10-volt fullscale input signal to obtain a 5-volt fullscale output. This output is routed to:

1.Recorder Output Resistor Network. It provides a jumper-selectable output of 0 to 10 mV, 0 to 100 mV, 0 to 1 V, or 0 to 5 VDC for a potentiometric re- corder.

Oxygen is strongly paramagnetic while most other common gases are weakly diamagnetic. The paramagnetism of oxygen may be regarded as the capability of an oxygen molecule to become a temporary magnet when placed in a magnetic field. This is analogous to the magnetization of a piece of soft iron. Diamagnetic gases are analogous to non-magnetic substances.

With the Model 755R, the volume magnetic susceptibility of the flowing gas sample is sensed in the detector/magnet assembly. As shown in the functional diagram of Figure 5-1 (page 5-2), a dumbbell -shaped, nitrogen-filled, hollow glass test body is suspended on a plati- num/nickel alloy ribbon in a non-uniform magnetic field.

Because of the “magnetic buoyancy” ef- fect, the spheres of the test body are subjected to displacement forces, resulting in a displacement torque that is proportional to the volume magnetic susceptibility of the gas surrounding the test body.

Rosemount Analytical Inc. A Division of Emerson Process Management

Circuit Analysis

5-11