transducer characteristics and types for agriculture

agriculture technology notes

1. Unit 2 Transducers

2. Definition Transducer is a device which converts energy in one form to another form It is a device which provides useful output in response to specific measurand The measurand may be physical quantity, property or condition which is measured.

3. The two major functions of transducer are To measure / To sense To convert the measure and value to a useful output

4. Transducer function

5. Measurement While selecting a transducer for any specific measurand , the following criteria should be considered Type of measurand Number of measurements Sensing element Transduction element Range of measurement

6. Conversion The conversion involves presentation of measured value in a specific format to the user For example, some transducers involve conversion of ac output from transducer element to dc output Some transducers convert analog signal to digital signal so that they can be interfaced to computer directly

7. Characteristics of transducers A transducer is normally used to sense the specific measurand and to respond only to that However, in some cases, measurand may even be calculated by their relationship to the measurand sensed by the transducer For example, pressure transducer measures pressure, displacement transducer measures displacement, acceleration transducer measures acceleration

8. However, displacement transducers can be used to measure position Displacement transducers can be used to measure velocity Acceleration transducers can be used to measure velocity The higher and lower limits of the measurand value form the range of transducer The range may be uni -directional, bi-directional or expanded The algebraic difference between the limits of the transducer is called the span of the transducer

9. For example, the span of -2 +10g accelerometer is 12g. Electrical characteristics Transducers normally produce analog output in the form of current, voltage ratio, voltage amplitude or variation of other parameters such as capacitance, inductance etc.,

10. The transducer with in-built rectifier to convert ac to dc voltage output will present ripple in the output If the transducer has integral amplifier, the amplifier characteristics such as noise, gain instability and recovery time are reflected at the output.

11. Static Characteristics Accuracy – It is defined as the difference between the indicated measurand value and the true value. It is expressed in percentage of full scale output (%FSO) Precision is defined as closeness with which measurements are distributed about their mean value. It is referred to as the degree of agreement on a set or group of measurements

12. Repeatability is defined as the ability of the transducer to reproduce output relation and same measured value, when it is applied consecutively under the same conditions in the same direction. Linearity is defined as the closeness of a transducer calibration curve to specify a straight line. Resolution – The output of transducer normally changes in small discrete steps when the measurand is varied over the range.