Difference between pressure transmitter and transducer 8

[RE52]

I need to now exact, what is the difference between pressure transmitter and pressure trancducer. thanx to any reply.

 

[obg]

As a general rule of thumb they both do the same thing. However some manufacturers call a current output type ie 4-20ma a transmitter and the voltage output types ie 0-5v a transducer. As a guide most users use transmitters with cable runs of 10metres and over.

 

[Ashereng]

Many transmitters can also be set to give either a 4-20 mA or 1-5V output. Example is the Rosemount 3051 line of pressure/DP transmitters.


"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[zdas04]

Guys, it's 1-5 mV not 1-5 V. I think the difference is in people's marketing literature.

David

 

[Ashereng]

David,

In my case, the transmitter does send a 1-5 V signal.

http://www.spartancontrols.com/libr...nt/Pressure/3051 Pressure Transmitter PDS.pdf

This is the Rosemount 3051 series.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[danw2]

The transducer converts the physical phenomenon to an electrical signal.

A transmitter provides a conditioned output signal.

A pressure transmitter always has a transducer internally, whether it's peizoelectric or capacitive or whatever.

A temperature transmitter converts the low EMF of a thermocouple (and does cold junction compensation) or converts the resistance of an RTD (by providing a regulated current to the RTD) to a conditioned output signal.

A conductivity transmitter provides excitation to the electrodes and provides a conditioned output signal.

 

[itsmoked]

1-5mV is what you might get out of a pressure sensor.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[zdas04]

Ashereng,
Rosemount documentation is usually excellent, but I'm a bit confused about this one. Since power = volts * amps, the power consumption on Page 9 says that at a constant 3mA load the power consumption is 18-36 mW which implies a voltage range of 6-12V. I find that odd of a 1-5 V output range.

I'm out of my depth here, buth I've always specified the "voltage signal" option for devices that had to sit in a area with an electrical classification of Class 1 Div 1 because they're classed as "intrinsically safe" (and the Rosemount 3051 has that classification). That would be true if it was a 1-5 mV 3 mA circut which would generate 3-15 micro W. It seems like it wouldn't be worth the PLC programming to switch from a 4-20 mA to a 1-5 V 3mA signal, just too little bank for the buck.

Maybe someone who doesn't see an electron as a really small droplet could set me strait here.

David

 

[danw2]

The Rosemount transmitter David is referring to (if he and I are reading off the same sheet

http://www.emersonprocess.com/rosemount/document/pds/3051.pdf)

is a 3 wire, low-power transmitter with 1-5Vdc output. There is no option for 4-20mA output on this transmitter.

Unlike the vast majority of field instruments, which are 2 wire loop powered (not 3 wire), and which drive 4-20mA through a 250 ohm resistor to get a 1-5Vdc drop, this 3 wire low power transmitter provides a voltage output (not a current output) that is just 1-5Vdc; not 1-5Vdc @ 3mA.

The 3mA that is the current component of the power consumption for this transmitter would be measured through the power supply + and common lines (2 of the 3 wires). But that 3mA is NOT the current flowing through the signal + and common lines. The signal + and common lines are strictly a voltage output, not a current output. The current in the signal + & common lines would be in the microamp range.

I was once told that the low power units were initially designed for the low power consumption requirements of pipelines, where there is frequently no utility power and units run on solar recharged battery banks.

With regard to your I/S (intrinsically safe) requirement, it isn't clear to me why you would have to use the low power model for I/S (I think it costs quite a premium). Yes, it is low power, but the 2 wire loop powered transmitters are rated I/S, even with their higher power consumption (22mA at 24Vdc).

Dan

 

[itsmoked]

I agree with danw2. You use a standard IS 4-20mA unit (thru barriers!) to your PLC. If you want a voltage-in to the plc you convert with a resistor as mentioned.

The reason the units are 4-20mA is so the unit itself can be powered by the first 3.99mA.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

"The reason the units are 4-20mA is so the unit itself can be powered by the first 3.99mA."

Well, almost. The self-detected failsafe mode is indicated by either a below or an above nominal range value, like explained below, either 3.85mA or 21.75mA.

So the transmitter's power is the first 3.84mA or thereabouts.

--- Rousemount 3051 manual pg 9 pdf) ----
Failure Mode Alarm
Output Code A
If self-diagnostics detect a gross transmitter failure, the analog signal will be driven either below 3.75 mA or to 21.75 mA to alert the user. NAMUR-compliant values are available, option code C4. High or low alarm signal is user-selectable by internal jumper.

 

[itsmoked]

Well thanks for the clarification danw2 but I was speaking generally since the OP never specified any particular transmitter. Certainly not a gold plated Rosemount. But again, nice to know.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JLSeagull]

zdas04 and danw2 covered transducers. Among the reasons for a 4-20 mA transmitter signal is that it is that the current loop does not require compensation for the signal wire resistance provided that sufficient voltage exists to drive the loads.

If itsmoked can be gentle, count me among the "gold plated" Rosemount fans. Although I work with clients who buy other transmitters, Rosemount is among the few "sole source providers" specified by many clients including those who buy Honeywell or other control systems.

 

[itsmoked]

Ha JLSeagull! NEVER!! AARGH matey!

Joking aside, Rosemount stuff is quality, for sure! I just hate it when a company reaches the status where they can charge a bunch extra just because of the name, while simultaneously shutting out little companies, (via spec writers covering their bottoms). But frankly I'd probably do it too if I knew the price didn't matter.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[obg]

Wow a promotional campaign! As I said at the beginning it has gotten rather confused. In Pure terms a transducer converts one form of energy to another, whilst a transmitter does what it says (sends out signals). However if you have a sensor of any type (or brand) it will have to contain both elements for you to be able to use the info from it. A rose by any other name huh.

 

[zdas04]

Obq,
There is a definition that I can get behind. With that definition there are no pressure transmitters except pipe, all of them convert a pressure to some sort of electrical signal before transmission so they are all transducers.

David

 

[JLSeagull]

zdas04, don't forget that pipe can convert the pressure to other pipe via a pneumatic transmitter too. I have not done that lately.

 

[kontiki99]

McGraw Hill Dictionary of Scientific and Technical Terms 3rd Edition 1984


Sensor

The generic name for a device that senses either the absolute value or change in a physical quantity such as temperature, pressure, flow rate, or pH, or the intensity of light, sound, or radio waves and converts that change into a useful input signal for an information gathering system; a television camera is therefore a sensor and a transducer is a special type of sensor.

Transducer

Any device or element which converts an input signal into an output signal of a different form; examples include the microphone, phonograph, pickup, loudspeaker, barometer, photoelectric cell, automobile horn, doorbell, and underwater sound transducer.



Oxford English Dictionary 2nd edition CD-ROM version

Sensor
A device giving a signal for the detection or measurement of a physical property to which it responds.

Transducer
Any device by which variations in one physical quantity (e.g. pressure, brightness) are quantitatively converted into variations in another (e.g. voltage, position).

IEEE Standard Dictionary 1993 (I only re-typed the first definition here)

Sensor
Device that responds to a physical stimulus and transmits a resulting signal.

Transducer
A device that is actuated by power from one system and supplies power in any other form to another system.

 

[JLSeagull]

Omega.com provides the following:
Pressure transducers are generally available with three types of electrical output; millivolt, volt and 4-20mA. Below is a summary of the outputs and when they are best used.

Millivolt Output Pressure Transducers
Transducers with millivolt output are normally the most economical pressure transducers. The output of the millivolt transducer is nominally around 30mV. The actual output is directly proportional to the pressure transducer input power or excitation. If the excitation fluctuates, the output will change also. Because of this dependence on the excitation level, regulated power supplies are suggested for use with millivolt transducers. Because the output signal is so low, the transducer should not be located in an electrically noisy environment. The distances between the transducer and the readout instrument should also be kept relatively short.

Voltage Output Pressure Transducers
Voltage output transducers include integral signal conditioning which provide a much higher output than a millivolt transducer. The output is normally 0-5Vdc or 0-10Vdc. Although model specific, the output of the transducer is not normally a direct function of excitation. This means unregulated power supplies are often sufficient as long as they fall within a specified power range. Because they have a higher level output these transducers are not as susceptible to electrical noise as millivolt transducers and can therefore be used in much more industrial environments.

4-20 mA Output Pressure Transducers
These types of transducers are also known as pressure transmitters. Since a 4-20mA signal is least affected by electrical noise and resistance in the signal wires, these transducers are best used when the signal must be transmitted long distances. It is not uncommon to use these transducers in applications where the lead wire must be 1000 feet or more.

 

[HaiKalyan]

Hi brother,
Theoratically, A transducer is the one which converts one from of energy to another form. In the present case, stritly speaking the pressure transducer is the one, which is converting the Pressure energy input to an Electrical form of energy i.e., either a Piezo electric type or capacitive type etc.,. This signal can be called as a Raw input signal for the control systems.
A transmitter (either pressure or any thing) is the one which converts (actually, amplifies)this raw electrical signal (which is very weak in magnitude) into another level which can be safely and accurately transmitted on a cable upto the control systems. This signal is normally very resistant to the noise signals, which normally induces into the original signal during transmission from the transmitter to the control system.

Hope this helps you to understand. Please feel free to contact for any further queries in this matter.

Regards