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1
1. INTRODUCTION
1.1. Theory of Operation
The instrument consists of a vibrating wire sensing element in series with a heat treated,
stress relieved spring which is connected to the wire at one end and a connecting rod at the
other. The unit is fully sealed and operates at pressures of up to 250 psi. As the connecting
rod is pulled out from the gage body, the spring is elongated causing an increase in tension
which is sensed by the vibrating wire element. The tension in the wire is directly
proportional to the extension, hence, the change in displacement can be determined very
accurately by measuring the strain change with the vibrating wire readout box.
Nylon Tie
Coil & Thermistor Housing
Instrument Cable
(4 conductor, 22 AWG)
Transducer Shaft
Transducer Housing
Alignment Pin
Alignment Slot
Figure 1 - Model 4450 Displacement Transducer
CAUTION: Do not rotate the shaft of the Displacement Transducer. This may cause
irreparable damage to the instrument. The alignment pin on the transducer shaft and
slot on the body serve as a guide for alignment.
2. INSTALLATION
2.1. Preliminary Tests
Upon receipt of the instrument, the gage should be checked for proper operation (including
the thermistor The Displacement Transducer normally arrives with it's shaft secured at
approximately 50% of it's range, by either a split PVC sleeve, (for transducers over
100mm (4 inch) range), or a nylon Tyrap, (see Figure 1). This holds the instrument in
tension thereby helping protect it during shipping. Remove this PVC split sleeve or Tyrap
before proceeding. Connect the gage to the Readout to take a reading (see section 3).
The reading should be stable and in the range of 4000 to 5000. When the nylon tie is
removed the reading should be in the range of 2000 to 3000 when the alignment pin rests
on the housing tube (see Figure 1).
When pulling the transducer shaft out to check for proper operation do not extend the
shaft more than the range of the gage!
Checks of electrical continuity can also be made using an ohmmeter. Resistance between
the gage leads should be approximately 180, ±10. Remember to add cable resistance
when checking (22 AWG stranded copper leads are approximately 14.7/1000' or
48.5/km, multiply by 2 for both directions). Between the green and white should be
approximately 3000 ohms at 25° (see Table B-1), and between any conductor and the shield
should exceed 2 megohms.
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