The following excerpts from Section 1.1.2 of “Sensors and Signal Conditioning, 2nd. Ed.” (John Wiley & Sons, 2001) may interest you:

“A transducer is a device that converts a signal from one physical form to a corresponding signal having a different physical form. Therefore, it is an energy converter. This means that the input signal always has energy or power, i.e. signals consist of two component quantities whose product has energy or power dimension. But in measurement systems, one of the two components of the measured signal is usually so small that it is negligible, and thus only the remaining component is measured.

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Since there are six different kinds of signals—mechanical, thermal, magnetic, electric, chemical and radiation (corpuscular and electromagnetic, including light)—any device converting signals of one kind to signals of a different kind is a transducer. The resulting signals can be of any useful physical form. Devices offering an electric output are called sensors. Most measurement systems use electric signals, and hence rely on sensors.

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Sensor and transducer are sometimes used as synonymous terms. However, sensor suggests the extension of our capacity to acquire information about physical quantities not perceived by human senses because of their subliminal nature or minuteness. Transducer implies that input and output quantities are not the same. A sensor may not be a transducer.

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The distinction between input-transducer (physical signal/electric signal) and output-transducer (electric signal/display or actuation) is seldom used at present. Nowadays, input transducers are termed sensors, or detectors for radiation, and output transducers are termed actuators or effectors. Sensors are intended to acquire information. Actuators are designed mainly for power conversion.”

[This means that whereas in sensors uncertainty is essential and ideally no energy is drawn from the system being measured, in actuators efficiency in the energy conversion is essential.

Nevertheless, the use of these terms is far from uniform and their use in some industry sectors can be quite different. For example, some current transducers are based on transformers that only involve electrical signals.

A sensor is a device which can quantitatively measure a certain physical quantity. A transducer is a device which converts one physical quantity to another from of physical quantity, e.g., acceleration to voltage or voltage to pressure. Therefore, a transducer can be a sensor when it is used to measure a certain physical quantity. But the transducer can also be an actuator when the (electrical) input is converted to, for example, force. So a transducer is more general than a sensor.   

sensor includes the circuit elements to obtain the particular electrical output from the output of transducer which it measures .

Transducer, may  used in sensor, if needed.

Transducer is something which converts one form of energy into other form where as sensor performs sensing only depending upon the quantity to be sensed. Sensor is a part of transducer generally the initial stage of transduction.

Transducer facilitate transduction of signal from one form to the other.

The following excerpts from Section 1.1.2 of “Sensors and Signal Conditioning, 2nd. Ed.” (John Wiley & Sons, 2001) may interest you:

“A transducer is a device that converts a signal from one physical form to a corresponding signal having a different physical form. Therefore, it is an energy converter. This means that the input signal always has energy or power, i.e. signals consist of two component quantities whose product has energy or power dimension. But in measurement systems, one of the two components of the measured signal is usually so small that it is negligible, and thus only the remaining component is measured.

…

Since there are six different kinds of signals—mechanical, thermal, magnetic, electric, chemical and radiation (corpuscular and electromagnetic, including light)—any device converting signals of one kind to signals of a different kind is a transducer. The resulting signals can be of any useful physical form. Devices offering an electric output are called sensors. Most measurement systems use electric signals, and hence rely on sensors.

…

Sensor and transducer are sometimes used as synonymous terms. However, sensor suggests the extension of our capacity to acquire information about physical quantities not perceived by human senses because of their subliminal nature or minuteness. Transducer implies that input and output quantities are not the same. A sensor may not be a transducer.

…

The distinction between input-transducer (physical signal/electric signal) and output-transducer (electric signal/display or actuation) is seldom used at present. Nowadays, input transducers are termed sensors, or detectors for radiation, and output transducers are termed actuators or effectors. Sensors are intended to acquire information. Actuators are designed mainly for power conversion.”

[This means that whereas in sensors uncertainty is essential and ideally no energy is drawn from the system being measured, in actuators efficiency in the energy conversion is essential.

Nevertheless, the use of these terms is far from uniform and their use in some industry sectors can be quite different. For example, some current transducers are based on transformers that only involve electrical signals.

let me explain by the Glucose sensor as an example:

Glucose oxidase is the receptor - it selectively reacts only with glucose and produces the hydrogen peroxide.

the working electrode is the transducer - it converts the chemical Information (hydrogen peroxide concentration) into an electrical information (corresponding sensor current).

the sensor constists of receptor and transducer. Sometimes the sensor electronics are also included in the term "sensor".

transducer:one form to other form

sensor:one form to readable form (electrical form)

sensor=transducer +signal conditioning circuit

1.thermo meter is sensor mercury in thermometer is transduction element 

2 

Sensors are almost always transducers but transducers are not necessarily sensors. A transducer is a device which converts signals from one form to another. This can include loudspeakers and linear positioners are well as physical quantity to electrical signal devices.

Generally, in electronics, a sensor is only the "sensible" side of a device: it converts a physical quantity into another form of physical quantity (resistance, capacitance, ...). Obviously, other physical quantities affect sensor output (like temperature or EMI) and their effect has to be negligible in comparison to the input physical quantity to convert. A sensor is generally not able to furnish energy at its output. So a conditioning circuit surrounds the sensor to have a signal (voltage, current, or both). Conversely, a transducer is a more complex device able to convert the input physical quantity into an output signal (voltage, current or both). Therefore, a transducer integrates the sensing element and the conditioning system able to furnish an output signal proportional to the input quantity.

i know that is too late. but you can refer to VIM document which gives standard terms which have agreement among european union and several countries in the world. for example sensor is the first device which is directly affected by physical phenomena.. but in the terms you will not see the word transducer you will see measuring transducer ... finaly... i recommend this document for all.

Sensor converts any physical quantity to electrical quantity. However Traducer makes the output of sensor meaningful so it can be used for further process/application. So in many cases, the sensor is part of transducer.

Transducer = Sensor+ Signal Conditioning Circuit

Sensor is a part of transducer, in other sense.

Hello! Everything written above is correct, but I would like to add a little.

If viewed from a common human perspective, then a “sensor” is a more general concept.

"Sensor" is a large set of semantic meanings which includes a transducer. Which consists, as already mentioned above, and of the sensor as well. But a transducer is a more definite concept. Therefore, it must be used more carefully. Of course, in specific technical areas there can be very precise definitions for the sensor and transducer and within this area you need to follow them.

But in reality, the word (concept) "sensor" is more convenient. It can be just a sensor, a transducer, a whole measuring system. For example. We can say that temperature sensors are installed on the wings of the aircraft. Everything is clear to everyone.

If we say that transducers are installed on the wings of the aircraft, then we need to open the topic further .....

Interestingly, there is a magazine "Sensors", but is there a magazine "transducers"?