1. Proximity Transducer System Operation
Topic Objectives:
You will be able to explain the general construction and operation of the proximity probe system
You will be able to find probe calibration values both mathematically, and through the use of calibration equipment
You will be able to identify the conditions that lead to problems with proximity probes, including probe cable length(s), supply voltages, types of target material, etc

2. Triaxial Cable
CENTER
CONDUCTOR
OUTER
SCREEN
INNER
SCREEN
INSULATION

3. Probe Numbering CABLE TIP ASSEMBLY FIXED LOCK NUT
P/N
S/N APRS

4. Extension Cable Numbering
P/N
Make comments on types of connector protection – boots, tape, NO electrical tape, etc
P/N

5. Proximitor SIGNAL OUTPUT ELECTRICAL LENGTH SIGNAL COMMON
TRANSDUCER POWER

6. Proximitor Operation EXTENSION CABLE AND PROBE PROXIMITOR <100mil
RF SIGNAL
EXTENSION
CABLE
AND PROBE
PROXIMITOR
DEMODULATOR
OSCILLATOR

7. Eddy Current Flow
CONDUCTIVE
MATERIAL
RF SIGNAL
EDDY CURRENTS

8. Small Gap
RF SIGNAL

9. Large Gap
RF SIGNAL

10. Changing Gap
RF SIGNAL

11. Demodulator Operation
INPUT
PROXIMITOR
OUTPUT

12. Proximity Probe Usage
RADIAL MOVEMENT
AXIAL MOVEMENT

13. Proximity Probe Used as a Keyphasor®
NOTCH

14. Verification of Proximity Probes
Probe response is verified by measuring and creating a calibration curve
Problems that can cause proximity probes to be out of tolerance:
probe cable length
power supply voltage
crosstalk and sideview conditions
target size and material

15. Proximitor Calibration Graph24 22
CHANGE IN GAP 20 18
CHANGE IN VOLTAGE 16 14
OUTPUT IN VOLTS - DC 12 10
Mention both overall average curve, and individual 10 mil quantities 8 6 4 2
mils 10 20 30 40 50 60 70 80 90
100
110
120
130
140
PROBE GAP

16. Proximitor Calibration Equipment

17. Proximitor Calibration Equipment Setup
DC VOLTMETER
-VT
INPUT
PROXIMITOR
EXTENSION CABLE
SPINDLE MICROMETER
TARGET
PROBE

18. Calibration of Scale Factor
Average Scale Factor (ASF) equals:
change in gap voltage
change in gap

19. Calibration of Scale Factor
(-18.0Vdc) (-2.0Vdc)
0.08in or 2.0 mm
= 200 mV/mil or
= mV/um

20. Component Mismatch Effects24 22 20
SHORT 18
CORRECT 16 14
OUTPUT IN VOLTS - DC 12 10 8 6
LONG 4 2
mils 10 20 30 40 50 60 70 80 90
100
110
120
130
140
PROBE GAP

21. Power Supply Voltage Effects24 22 20
-24V SUPPLY 18 16 14
OUTPUT IN VOLTS - DC 12
-16V SUPPLY 10 8 6 4 2
mils 10 20 30 40 50 60 70 80 90
100
110
120
130
140
PROBE GAP

22. Probe Crosstalk

23. Sideview Effect

24. Effects of Target Size
YES NO

25. Target Material Effects24 22 20 18 16 14
OUTPUT IN VOLTS - DC 12 10 8 6
4140 STEEL
TUNGSTEN 4
ALUMINUM
COPPER 2
mils 10 20 30 40 50 60 70 80 90
100
110
120
130
140
PROBE GAP

26. Review Questions
Q1. The three parts of a proximity transducer system are: a. b. c.
Q2. The ruggedised Proximitor cable used is comprised of what three components?
____________, ____________, and ________________.
Q3. What is the electrical length of the following probe?
______.
Q4. What is the electrical length of the following extension cable?
______.
Q5. What is the total electrical length required by the following Proximitor?
______.
Probe
Extension cable
Proximitor
outer screen
inner screen
center conductor
0.5M
4.5M
5.0M

27. Review Questions
Q6. The Proximitor must be supplied with a dc voltage between _________,
and _________.
Q7. An ____ field is created around the probe. It extends away from the face of
the probe for linear range of at least _______.
Q8. When a conductive material is within range of the probe, what kind of
electrical flow is induced in the surface of that material? _____________.
Q9. A Proximitor must be calibrated to suit the ________ it has as a target.
Q10. The dc output from the Proximitor will become less _________ as the target
moves closer to the probe.
Q11. A proximity system frequency response is from ________ to _______ and
its output may contain an ____ and a ____ component.
-17.5 Vdc
-26.0 Vdc RF
80 mils
eddy current
material
negative
0Hz(dc)
10KHz ac dc

28. Review Questions
Q12. Name three applications for a proximity transducer system. a. b. c.
Q13. Calculate the scale factor (sf) from the following: 90mils = -18.5Vdc,
10mils = -2.25Vdc Is it within tolerance?
Q14. Name six reasons why a proximity system could be out of tolerance.
a d.
b e.
c f.
Thrust measurement
Vibration measurement
Keyphasor
203mV/mil
Yes, 1.5% error
Incorrect supply voltage
Mismatched components
Incorrect target material
Crosstalk
Sideview
Incorrect target size

29. Proximity Transducer System Operation
Topic Objectives Revisited:
You will be able to explain the general construction and operation of the proximity probe system
You will be able to find probe calibration values both mathematically, and through the use of calibration equipment
You will be able to identify the conditions that lead to problems with proximity probes, including probe cable length(s), supply voltages, types of target material, etc