Answer / carl_ellis

If this is not SIS (safety instrumented), the 4-20mA from a
single flow transmitter can feed a separate I/O modules (4-
20in, relay out) an alarm module and a separate interlock
module.

Or, depending on the converter/transmitter model, most
magmeters have at least one assignable relay output, some
have two relay outputs.

I've always used orifice flange unions that have only one
set of taps. There might be a double tap flange unions, or
I suppose you can drill and weld the pipe for taps. But
again, unless this is SIS, why would you? Decisions made
on a 4-20mA flow signal on a PLC?DCS/Controller/I?O modules
can do multiple functions.

If your situation is SIS, you should state that.

Carl Ellis
Measure First

Answer / carl_ellis

It seems you are using a flow meter's relay(s) to generate
alarm signals at various amplitudes: low, low/low, hi,
hi/hi.

The flow meter doesn't really use these alarm signals
itself, rather it generates the alarm signals and provides
the alarm signals to other devices, for whatever purpose,
alarm, annunciation or an interlock.

There might be a flow meter with 3 alarm relays. I don't
know. That's a shopping issue.

Most places will use a PLC, a controller or a DCS to
generate alarms from the analog flow signal.

But if your flowmeter doesn't have enough relays, then use
a "DC alarm trip" I/O module with the flow meter's 4-20mA
analog output.

The modules have an analog input and one or two relay
outputs with adjustable setpoints. There's probably a
dozen models on this page:
http://www.api-usa.com/signalconditioners_alarms.php

These I/O modules are not used "in a magmeter", they're
external I/O modules.

They place a small burden resistance in the 4-20mA circuit,
need an enclosure and AC or DC power to operate, but they
accomplish the task of providing multiple alarms at various
setpoints.

The 4-20mA signal is wired in series with the I/O module
and any other receiver devices.

Carl Ellis
Measure First

Answer / thiagaraj

@CARL ELLIS.. Thanks for your response.In case of using
Alarm (or) Interlock it was a normal practise that we
use ''LOW''LOWLOW'' (OR) ''HIGH''HIGHHIGH'' signal in the
same instrument(orifice etc)..If i need to
use ''LOW''HIGH''LOWLOW'' in the same Instrument is it
possible to use these 3 alarms in a single instrument(flow
transmitter )..If yes is it can be used in Magnetic flow
meter ..pls state its advantages and disadv also.pls clarify

how level can be measured in open tank with reference to pressure

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