Furuno FCV-1200L - 7 Testing Transducer; Checking Transducer with Multimeter; Checking Impedance at Resonant Poit

38
POT
Transducer
SW
R
S.G.
Oscilloscope
1
2
Signal Generator
7. TESTING TRANSDUCER
The transducers are classified into electrostriction type and magnetrostriction type.
Generally the transducer elements of the electrostriction type are made of barium titanate, and the
magnetrostriction types are made of ferrite.
Those are shown with the alfa-numeric after frequency number of the transducer type, For example;
50B - 6: "50" shows frequency and "B" means barium titanate.
28F -18: "28" shows frequency and "F" means ferrite.
7.1 Checking transducer with multimeter
Since electrostriction type of the transducer equivalent to the capacitor electrically, checking method
of the transducer is the same as that of the capacitance check using a capacitance meter.
Following table shows a reference value of a transducer.
Transducer Type Capacitance Transducer Type Capacitance
50B-6/50B-6G 7500 pF 200B-5/5S 2560 pF
50B-12 8500pF 200B-8 3200pF
88B-8 3200pF 200B-8N 8000 pF
200B-8B 5500 pF
Note: Capacitance including 10m cable (100pF/m)
The magnetrostriction type of the transducer is driven by a coil winding a transducer , therefore, the
conductance of coil may be checked by the multimeter.
The transducer type marked "H" has matching transformer inside; for example: 150B-12H.
Therefore, it should be checked as magnetrostriction type even though it is electorstriction type.
7.2 Checking impedance at resonant point
Figure 7.1 shows the impedance check circuit.
Figure 7.1 Impedance test circuit
Procedure to check impedance;
1. Set the SW to #1.
2. Set the output frequency of a signal generator to the resonant frequency of the transducer.
3. Measure the voltage across the transducer with an oscilloscope.
4. Set the SW to #2 and adjust the potentiometer so as to obtain the same voltage measured
in step 3.
5. Measure the resistance of the potentiometer. This resistance may be considered the impedance of
the transducer at the resonant frequency.
Note: the impedance of the transducer differs with measuring condition, i.e., in air or in water.
The tables 7.1/7.2 show the impedance and resonant impedance of the transducer in water.