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Transducer or Transmitter ?

05/13/2009 6:20 AM

Is it technically correct to say-Pressure transducer and pressure transmitter is same ?

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#1

Re: Transducer and transmitter ?

05/13/2009 6:41 AM

Hi there,

You are going to open a can of worms with this one!

Technically it is NOT correct to say that a transducer and a transmitter are the same.

A transducer coverts one type of energy of physical atrribute to another.

A transmitter sends information to a receiver.

The transducer part of the pressure transmitter might be a piezoelectric crystal, that changes electrical energy as pressure (force energy) is exerted upon it.

The transmitter consists of all the amplifiers and electronics that get the signal down the wires to your input card from the crystal.

My two cents worth. :)

Regards,

Craig

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Guru
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#4
In reply to #1

Re: Transducer and transmitter ?

05/13/2009 10:20 AM

Good enough for me!

regards,

Vulcan

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#2

Re: Transducer and Transmitter ?

05/13/2009 7:56 AM

I fully agree with Craigza...

And its the best explanation in short about transducer & transmitter.

Thanks & Best REgards

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#3

Re: Transducer and Transmitter ?

05/13/2009 9:21 AM

i think the confusion may arise because both devices are used to " control " other functions in the system..if my memory serves me today

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#5

Re: Transducer or Transmitter ?

05/14/2009 7:56 AM

In many hydroacoustic applications, a transducer can be used as both a transmitter and receiver. The typical marine echosounder, i.e., fish finder, depth indicator, ustilizes a single ceramic transducer to transmit an acoustic pulse downward in the water column. Shortly thereafter, the transducer is switched to the receiver circuitry, responds to the echos returning from the seabed, and these signals are processed by the receiver. So, a transducer (the device) can be defined by it's application; transmitter, receiver, or transceiver.

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#6
In reply to #5

Re: Transducer or Transmitter ?

05/14/2009 8:31 AM

I forgot to mention: An acoustic transducer operating in the transmit-only mode is referred to as a Projector and one operating in the receive-only mode is referred to as a Hydrophone or Hydrophome Array. When a device is operating in a transmit/receive mode is simply referred to as a Transducer.

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#7

Re: Transducer or Transmitter ?

05/14/2009 1:55 PM

hi shashi

Here is the basic difference that I would like to present you

It is the response time that matter between transducer and transmitter.

FIRST ORDER RESPONSE TIME

Response time as defined by ISA Standards and Practices for Instrumentation, 9th Edition, Volume 2, 1988 "is an output expressed as a function of time, resulting from the application of a specified input under specified operating conditions".

  • First order time constants represent the time required for a pressure transmitter to achieve an output of 63% to a step change input pressure. Five time constants are required to achieve an output of 99.9 % to a step change input.

Pressure sensing type

Sensor

Micro P

Signal conditioning

TransducerYesNoNo
Analog transmitterYesNoYes
SMART transmitterYesYesYes

Transducer are more faster in response than analog and Smart transmitter .

I have seen in centrifugal Inersollrand compressors for antisurge system they are using pressure transducer so as to get faster input response.

Regards

Adil

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#8

Re: Transducer or Transmitter ?

05/16/2009 7:18 AM

Dear Mr. Tiwary.

Pl find undermentioned the para i found reading one of the website which tries to tell us the difference between transducer & transmitter.

What is the difference between a transducer and a transmitter? (FAQ - Pressure)

Transducers

Transducers are voltage-output devices that can be used with simple signal conditioning but are more sensitive to electromagnetic interference. The electrical resistance of the connecting cable can cause significant errors if the cable is long. They require three or four connecting wires to supply power and deliver the output signal.

Transmitters

Transmitters are current-output devices and may have two or three wires. Where two wires are used to both receive power and transmit an output signal, significant cost savings can be made where long cables are needed. They are frequently scaled to vary from 4 mA to 20 mA as the pressure varies from minimum to maximum. Thus the on-board electronics has to be capable of operating with a maximum current drain of less than 4 mA. Being 'current driven', the in-built circuitry controls the voltage across the transmitters two terminals to ensure that the appropriate pressure-proportional current is maintained irrespective of line resistance up to a specified limit. Thus these devices are very suitable for use with long cables and are much less susceptible to electromagnetic interference than voltage-output transducers. Sometimes called current loop or serial devices, additional displays at different locations can easily be included in the loop without degrading the output signal. Such devices normally suffer no significant degradation of signal output with distance.

Digital output transmitters normally contain a microprocessor which converts measured pressure values into digital codes which are transmitted to a remote receiver, or 'host', via wires, optical fibres or radio. There are a number of standard systems available, such as Fieldbus (IEC 1158) and HART, the latter having the facility to operate in combination with the more traditional 4 mA to 20 mA current-output systems. Beyond supplying pressure values, digital transmission can include diagnostic information, status and alarms and can also facilitate remote reconfiguration of transmitters.

NOw the undermentioned is another explanation of the difference bwteen pressure transducer & pressure transmitter..

What is the difference between a pressure transducer and a transmitter



Unfortunately if you are looking for a black and white answer to this question it is not as simple as that. Distinguishing between a pressure transducer and a pressure transmitter can depend upon which country you are working in and which manufacturer you are dealing with. As with a lot of engineering terminology the original definitions have become a little blurred and have not always been used in the way that was originally intended.

A pressure transducer is fundamentally any device that converts an applied pressure into an electrical signal. There have been many different types of pressure transducer developed over the years such as bonded foil, thick film, thin film & semiconductor strain gauge to name just a few. All of these sensing technologies are pressure transducers and they provide an electrical signal typically a millivolt output signal which varies with changes in pressure when connected to an appropriate power supply.

Typically a pressure transducers output signal is one generated by the primary sensing element. Since it is difficult to achieve tight electrical tolerances with the sensing elements during manufacture it is often necessary to add a circuit to trim the zero & span offsets and compensate for errors over the operating temperature range. However the pressure transducer still retains the natural characteristics of the particular sensing technology employed such as linearity, hysteresis, repeatability, stability and frequency response. In fact these are the main reasons for using a pressure transducer which apart from the compensation circuitry are the purest form of pressure sensor.

It is possible to source pressure transducers without compensation electronics which are also known as pressure capsules, modules or headers, which are mostly used by instrument manufacturers who utilise their own micro-electronics to compensate the pressure transducer.

If the electrical connections are short, such as in the laboratory or inside an electronics enclosure the pressure transducer is more desirable, since it is smaller because it has virtually no pcb electronic components inside and there are none or very few active electronic components that can be upset by electromagnetic interference.

So what happens when you want to run the electrical output signal of a pressure transducer over long distances? In the past this was required when engineers started to automate process plants such as power generation plants where they wanted to replace pressure gauges with pressure sensors. The distance was too far between the control system and the measurement point to use a pressure transducer, because the signal losses and interference of the cables would be too great. Therefore the transducer output signal needed to be amplified to transmit the transducer signal over large distances around the plant without attenuation. Many types of amplified signals have been developed over the years as electronics have advanced and power considerations have changed but the 2 wire 4-20mA current loop output has long been accepted worldwide as the main method for transmitting pressure transducer signals over long distances and is still the most requested output signal particularly in the process control industry.

So a pressure transmitter is simply a pressure transducer with some extra electronics to transmit a 4 to 20 mA output signal. At first pressure transmitters would only be found in large process plants and the sensors were bulky and relatively expensive. In recent years other industries have adopted the 4-20mA output signal pressure transmitter because it only needs 2 wire connections and solid-state electronics has shrunk the size and cost of these pressure sensors so much, that it is now difficult to tell the difference between a pressure transducer and transmitter by just looking at its size and shape.

The shrinking of the size of a pressure transmitter is when the definitions started to get blurred between pressure transducers and transmitters. The divisions have become even more blurred with amplified voltage output pressure transducers. They have the signal strength to transmit over greater distances than a strain gauge output pressure transducer but use less power than the 4-20mA output signals.

One of the other benefits of pressure transmitters and high voltage output pressure transducers is that they incorporate zero & span adjustment potentiometers so that the pressure sensors can be easily calibrated.

So today the general rule of thumb is that if the pressure sensor has a millivolt (e.g. 30mV or 100mV) or non-amplified output it is a pressure transducer. If the pressure sensor has a voltage (e.g. 0-5Vdc, 0-10Vdc or 1-5Vdc) output it is an amplified voltage output pressure transducer. If a pressure sensor has a current loop output (e.g. 2 wire 4-20mA or 3 wire 0/4-20mA) it is a pressure transmitter.

However you should be aware that you will find plenty of contradictions to this rule of thumb between manufacturers so always check the actual signal output on the data sheet where there should be no ambiguity and it is best not to rely on the descriptive name to define the output signal.

Hope now something must be clear in regards to transducer & transmitter.

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#9
In reply to #8

Re: Transducer or Transmitter ?

05/16/2009 7:30 AM

Dear Mr. Vikramnegi,

Yes, Basic understanding of transducer & transmitter is now clear.

Thanks

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Guru
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#10

Re: Transducer or Transmitter ?

05/16/2009 7:34 AM

I suddenly remembered that this question was asked before.

http://cr4.globalspec.com/thread/35601#comment370304

regards,

Vulcan

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#11
In reply to #10

Re: Transducer or Transmitter ?

05/17/2009 3:03 AM

hahaha..

u r right Vulcan...

and i see that one of the memeber earlier have cut & paste the same piece of information which i did in my last posting....

seems we both struck the same website...lol GOOGLE SEARCh...lol

Thanks & best Regards

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India - Member - ADIL MOULA Engineering Fields - Instrumentation Engineering - Adil Moula

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#12
In reply to #10

Re: Transducer or Transmitter ?

05/17/2009 4:31 AM

thanks Vulcan

but you should have told in first answer ,I would have not dug new things .

anyway it will upgrade the knowledge.

regards

Adil

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#13
In reply to #12

Re: Transducer or Transmitter ?

05/17/2009 7:26 AM

It's just my age showing .

I was scanning my list of discussions and stumbled on it. Completely forgot about it. I guess this is one reason never to unsubscribe.

regards,

Vulcan

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