Expert: Marc Ebelini - 1/31/2007

Question
Hi,
   How about the way they are measured. Does the pressure transmitter measure amps and the transducer in volts per volts?
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The text above is a follow-up to ...

-----Question-----
Is there a difference between an oil pressure transducer and an oil pressure transmitter? Do both work on A.C power or D.C power?
-----Answer-----
Not that I am aware of. They both do the same thing so I think it's a matter which way you look at it.
A transducer transmits the information to the host. While the common method is resistance, there are other forms of collecting data. A pressure transducer changes resistance relative to the pressure applied. Likewise for a temperature transducer.  The host can be a gauge reading the resistance change and calibrated accordingly. The information can also be applied to an electronic device for evaluation. Typically DC voltages are used. AC devices are rare because they are more costly although more accurate. If timing is involved the changes take place in the form of pulses. Sometimes referred to as choppers. Visualize a paddle wheel spinning inside a fuel line caused by the flow of fuel. Each blade is magnetized so each time it passes a transducer the applied voltage is pulsed. The amount of pulses are translated to flow rate. Whenever flow rates are slow whether air, fuel or water paddles wheels or spinning devices are used. Pitot tubes are used when the flow rates are higher. Airplanes use pitot tubes for airspeed. Smaller airplanes apply (transmit) the pressure directly to the airspeed gauge. High performance ones feed it to transducers to be translated.
Simply put, a transducer is any device that translates information to another format and allows it to transmitted to another location. As stated above it need not be electrical as in the case of the pitot tube.
Transmission can take place in air, water, infra red and radio. Capillary tubes can be used to obtain oil pressure but they are not transducers since the information is not translated to another form.
Hope this has been of some help to you.  

Answer
Now apparently you want to know about pressure sensors. Which of course are part of the transducer. Reading your question you obviously need to learn basic electronics. The "volts per volts was the clue" Let me assume you saw some place about "ohms per volt" This is used when determining the sensitivity of a Volt/Ohm meter. Referred too as a VOM.
The higher the resistance the more sensitive the meter. Looking at the lower bottom corner of the VOM meter the standard type will read 20,000 ohms /volt. Now back to the transducer. Pressure applied to a diaphragm can cause a resistance change by various means to lengthy to get into here. The pressure can also be used to move a inductive devise that would use AC instead of DC. When the DC is applied and the resistance changes then there will be a change in the current. This change is calibrated to reflect the pressure applied. Visualize a diaphragm moving a potentiometer, as the resistance changes so will the current.
In the ac device the inductor values changes that shifts the frequency in the circuit. Just like tuning the slug on a radio transformer. In your automobile your fuel gage works like a pressure transducer except that a float moves the potentiometer to change the current to indicate fuel level. In high pressure transducers special pressure sensitive resistors are use. FYI knowing the sensitivity of your measuring device can be very critical in obtain the proper reading. Hope this has helped?