Inline vs non inline instruments

[shahyar]

Hi,
What is the definition of "inline Instruments" and "non inline Instruments"?
I have found even Transmitters and some TG's in our inline instruments list.
Thanks for replies.

 

[jmw]

I usually interpret inline to mean installed in the main pipeline and not in a by-pass (slip stream).
Online is more tricky because it could mean functioning (as opposed to offline) or it could mean a process measurement rather than a lab measurement.
But this is a grey area because some people use the terms with less discretion and I like to clarify whether it's me telling or me being told.
Equally loosely used are the terms transmitter and transducer so i like to refer to a transmitter as (usually) providing a scaled or conditioned output and a transducer as device giving a raw output that is processed in secondary remote electronics.

JMW

http://www.ViscoAnalyser.com

 

[Engineer6512]

I always made the distinction that an inline instrument was one which the actual process fluid flowed through. I always try to go the "non-inline" route, as performing a repair or calibration of your instrument usually requires that it be isolated from the main process. If it is inline, that means shutting down the process temporarily if there is no way to bypass the instrument.

http://www.SteamPlantEngineering.com

- Discussion & resources for professionals in the Power Generation Industry

 

[JimCasey]

In most cases an inline instrument takes a direct measurement, while an instrument that is not inline takes a measurement that is used to infer the actual measurement that you seek. Example: Those doppler clamp-on flowmeters that calculate a flow-rate based on the observed shift of transit time.

 

[jsummerfield]

My two copper coins call this semantics. The definition depends upon the context to some degree. As a control systems design engineer my schedules often includes inline and online for separate tracking. This context is senseless to a plant operator.

Besides maintenance, other groups such as piping designers need dimensional information for inline instruments. The flow is through an inline instrument such as a control valve or many flow measurement technologies. Regard a relief valve as an inline instrument.

A thermowell inserts into the piping. However, piping designers only need to know the connection size. Thus, I do not regard a thermowell as an inline instrument if the driving force between the categories applies to dimensional data. However, construction is more interested in hydrostatic testing. Perhaps the thermowell needs to be installed during flushing and hydrostatic testing. In such a case, the thermowell would likely be regarded as inline.

Pressure instruments are online. These installation of offline instruments may be direct coupled, close coupled or remotely mounted. Let's address analyzers separately.

Electrical instruments and accessories associated with inline and online instruments are offline instruments. Offline instruments may include the transmitter for a Coriolis flow meter, a temperature transmitter that is not directly mounted to the temperature sensing element, etc.

A process gas chromatograph is an online analyzer. A sample probe falls into the thermowell class regarding inline verses online. The sample flows through tubing and the probe is inserted in the line. Piping does not need dimensions and you do not want construction to flush through or hydrostatically test the sample point. However, an offline analyzer would be the laboratory chromatograph instead of the analyzer permanently coupled to the process.

Then there is the equipment basis for online verses offline. Three pumps may be installed with a lead pump, lag pump and standby pump. These may be selectable for any of three pumps to be each status. If the lead cannot maintain a level then the lag starts, and only when the lead and lag cannot maintain the level then the standby starts, etc. The lead might be regarded as online. For such an automated sequence the other pumps would require the block valves to be lined up. With two or more pumps and only one with the valves lined up, the additional pumps would be off line.

John

 

[jmw]

I think that JimCasey illustrates well the problem with the looseness with which some of these terms have come to be used. In this case I would say that inline and offline are not the terms to use for an ultrasonic meter. More often the term used is "non-invasive" since the instrument can often be claamped to the outside of a pipe.

But what about this measurement of transit time?

How many measurements measure the exact property we are looking at? A trubine flowmeter doesn't measure flow either. It responds to velocity profiles. Volume flow is determined from the pipe cross-section at the rotor. In a mass flow meter the mass flow is determined from phase angles consequent on twisting. An ultrasonic meter measure velocity of sound. In a thermal mass meter we measure something else yet again. What we don't actually do is measure directly what we are interested in but the effect it has on something else that we can quantify. Temperature sensors: apart from actually only rporting their own temperature, you measure voltage or resistance.

Concentration measurements can be based on a variety of different properties measured and then related to the parameter of interest; gamma ray absortion, vibrating element density measurement (where you actually measure the resonant frequency and relate that to density), refractometers etc. etc. In fact, a sizeable number of measurements are actually "indirect" i.e. you measure one property to infer another.

We do need to be particular and consistent in how we describe "things" but it is a poor example set by ISA to in one handbook on instruments refer to density measured by the "coriolis effect" which is nonsense and makes the situation worse, not better.

It does mean that where there is a possible ambiguity one needs to explain ones own glossary, just as in an equation you have to define what each symbol represents, so too you have to explain how you are using a particular term if you suspect there is potential for misunderstanding, and probably often when there is only a slight chance.

JMW

http://www.ViscoAnalyser.com

 

[shahyar]

Thanks, I got my answer.