Fluid-components-international FR73B Manual General Information User Manual download pdf

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Model FR78B Flow Switch/Monitor

CHAPTER 1 - GENERAL INFORMATION FLUID COMPONENTS INTL

1. General Information

Description

This document explains the operating principle of the Model FR78 Basic Low-Flow Switch/Monitor (see

Figure 1-1). The following pages also present the recommended procedures for the installation, operation,

maintenance, and troubleshooting of the Model FR78B.

The Model FR78B is an instrument that is capable of detecting liquid or gaseous environments. The instrument

has field adjustable alarm set points for control of the media.

Flow Element

The operational part of the flow element consists of two Resistance Temperature Detectors (RTD's) and one low

power heater. The heater is positioned adjacent to the Active RTD and will raise it's temperature above the process

ambient while the other RTD (Reference) will stabilize near the process temperature. This arrangement produces

a temperature differential between the two RTDs that is measured and converted into an analog voltage signal.

The temperature differential is greatest when the media is not flowing (no flow). As the process media begins to

flow, forced convection cools the Active RTD and reduces the temperature differential between the two RTDs.

Control Circuit

The basic functions of the control circuit are to provide power to the flow element, measure the resistance

differential (DR) between the two RTDs, condition the sensing point signals, and provide relay alarm contacts for

customer uses.

A Double Pole Double Throw (DPDT) relay is available in the instrument for connections to the customer alarm

systems. The relay outputs can be set to be either open or closed when the sensing point is at low or no flow and

closed or open when the sensing point is at high flow.

The place where the relays change state will vary depending on the type of media, as well as gas or liquid

turbulence. Therefore the instrument has field adjustable alarm set points.

Figure 1-1. FR78B Fast Response Flow Switch/Monitor

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Doc. No. 06EN003281 Rev. -1 - 1 Model FR78B Flow Switch/MonitorCHAPTER 1 - GENERAL INFORMATION FLUID COMPONENTS INTL1. General InformationDescr

FLUID COMPONENTS INTL CHAPTER 1 - GENERAL INFORMATIONModel FR78B Flow Switch/Monitor1 - 2Doc. No. 06EN003281 Rev. -• Sensing/Flow Element RangesWate

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Fluid-components-international FR73B Manual General Information User Manual