How to Calibrate a Proximity Probe with the AT-2040
The AT-2040 Portable Vibration Calibrator can be used to test proximity probe and driver systems by supplying the required driver power, reading gap voltage, and supporting both linear DC checks and dynamic AC vibration tests.
Typical proximity probe checks
- Gap voltage verification
- Incremental scale factor, usually mV/mil
- Linear range check
- Probe/driver wiring confirmation
- Dynamic AC response at fixed gap
- PDF and CSV report support
What the AT-2040 does during a proximity probe test
A proximity probe system measures the distance between the probe tip and a conductive target, usually producing a negative DC gap voltage with an AC vibration component when the target is moving.
With the PRX-100 Proximity Probe Adapter Kit, the AT-2040 can position a probe in front of a 4140 steel target, power the driver with −24 V, read the driver output, and allow the operator to record voltage versus distance.
AT-2040 proximity support
Linear test vs. dynamic test
Proximity probes can be checked two ways. The linear test verifies voltage output across the probe range. The dynamic test checks AC response while vibrating the steel target at a fixed gap voltage.
Linear DC test
The probe gap is adjusted with the micrometer in known increments, such as 10 mil steps. The operator records the driver voltage at each position and calculates the incremental scale factor across the linear range.
- Best for checking full probe/driver linearity
- Shows ISF across the range
- Can be performed with or without shaker vibration
- Uses the proximity probe spreadsheet template
Dynamic AC test
The probe is set to a fixed gap voltage and the shaker moves the 4140 steel target to simulate shaft motion. The system reads the AC voltage response during vibration.
- Useful for checking AC response
- Performed at a fixed gap voltage
- Can be run in manual or automatic mode
- Does not show full-range linearity by itself
Prepare the probe, driver, target, and fixture
A proximity probe calibration depends on mechanical alignment, correct driver wiring, and a stable target. Use the correct probe clamp, mounting legs, micrometer, and 4140 steel target for the probe being tested.
Confirm probe system details
Check the probe and driver datasheet for linear range, recommended gap setting, scaling factor, probe diameter, cable requirements, and driver wiring.
Install the 4140 steel target
Screw the steel target into the reference accelerometer location. The target simulates the conductive shaft or machine surface viewed by the proximity probe.
Build the PRX-100 fixture
Install the panel adapters, mounting legs, micrometer, mounting bar, and correct probe adapter arm so the probe can move toward and away from the target.
Install the proximity probe kit
The PRX-100 kit holds the probe and micrometer in position so the distance between the probe tip and steel target can be adjusted in controlled increments.
Install the target
Screw the 4140 steel target into the reference accelerometer mounting location.
Add panel adapters
Install the panel adapters into the front-panel locations marked for the proximity probe kit.
Install the micrometer
Insert the micrometer through the mounting bar and lightly secure it with the set screw.
Select the probe clamp
Use the adapter arm that matches the probe diameter, such as 1/4 inch, 3/8 inch, 6 mm, 8 mm, or 10 mm.
Install the probe
Insert the probe through the mounting bar and clamp it securely in the adapter arm.
Align the assembly
Install the correct mounting legs and thumbscrews so the probe can contact the target and move across the range.
Connect the proximity probe driver
Connect the proximity probe driver output to the AT-2040 Proximity Probe Driver Input. The AT-2040 supplies −24 V power to the driver and reads the driver signal.
On the AT-2040, open Vibration Output, select the Channel button, and choose Prox. The screen can show gap voltage for the proximity probe input and displacement units such as mils, mm, or µm.
Driver input wiring
- SIG — Driver signal output
- COM — Common
- −V — −24 V driver power
Confirm wiring against the probe driver datasheet before powering the system.
Run a linear DC proximity probe test
A linear test checks the relationship between probe distance and output voltage over the operating range. This is the preferred method when verifying incremental scale factor.
Linear test steps
Common 200 mV/mil example
A 200 mV/mil probe/driver system changes approximately 2 V for every 10 mil change in probe gap. For example, a reading near −1 V at 10 mils and −3 V at 20 mils would represent approximately 200 mV/mil.
Voltage change ÷ Gap change = ISF
2.0 V ÷ 10 mils = 0.2 V/mil
0.2 V/mil = 200 mV/milLinear proximity probe test table
The actual voltage values depend on the probe/driver system and gap direction. The purpose of the table is to record voltage versus distance and calculate incremental scale factor.
| Probe gap | Example voltage | Voltage change | Calculated ISF |
|---|---|---|---|
| 10 mils | −1.0 V | — | — |
| 20 mils | −3.0 V | 2.0 V over 10 mils | 200 mV/mil |
| 30 mils | −5.0 V | 2.0 V over 10 mils | 200 mV/mil |
| 40 mils | −7.0 V | 2.0 V over 10 mils | 200 mV/mil |
| 50 mils | −9.0 V | 2.0 V over 10 mils | 200 mV/mil |
Run a dynamic AC proximity probe test
In a dynamic test, the shaker simulates shaft motion by moving the 4140 steel target while the probe is held at a fixed gap voltage. This checks the AC response of the probe/driver system.
This can be useful when verifying a monitoring channel or checking how a probe/driver responds to a known vibration input at a selected gap.
Dynamic test checklist
- Install the PRX-100 fixture and steel target
- Connect SIG, COM, and −V to the driver input
- Select the Prox channel
- Set the probe to the recommended gap voltage
- Select the frequency and displacement amplitude
- Start the test and observe the AC response
Set the probe near the center of the linear range
For a dynamic test, the probe should normally be set near the recommended gap voltage or near the center of its linear range. Always use the probe/driver datasheet when available.
Example
If the recommended gap is 50 mils, the approximate center voltage is:
(50 × 0.2) − 1 = 9 V
For a negative proximity system:
Approximate gap voltage = −9 VdcImportant
This is a practical example for a common 200 mV/mil system. Always follow the specific probe and driver datasheet because linear range, polarity, and recommended gap may vary by manufacturer and model.
What to watch during the test
During a proximity probe test, the operator should monitor gap voltage, displacement, signal behavior, and mechanical alignment.
Gap voltage
Confirms the probe is positioned in the expected part of the driver’s linear range.
Incremental scale factor
Shows the mV/mil relationship across the measured range during a linear test.
Displacement units
Use mils, mm, or µm depending on customer requirements and probe system documentation.
Target alignment
Misalignment, loose clamps, or probe movement can cause unstable or incorrect readings.
Record and export proximity probe results
For linear proximity probe testing, record voltage readings at each gap increment and calculate the incremental scale factor using the proximity probe spreadsheet. For dynamic tests, record the fixed gap voltage, vibration level, frequency, and AC response.
The AT-2040 can also store test records and export reports for documentation, review, or customer delivery depending on the test workflow.
Suggested record items
- Probe and driver model
- Serial numbers
- Probe gap positions
- Measured DC voltages
- Calculated mV/mil scale factor
- Dynamic test frequency and amplitude
- Technician, date, and customer information
Acceptance criteria are controlled by your procedure
The AT-2040 provides the measured values needed to evaluate the probe and driver. Pass/fail decisions should be based on the probe/driver specification, customer tolerance, laboratory uncertainty, and applicable decision rule.
Common criteria
- Incremental scale factor tolerance
- Linear range limits
- Gap voltage at reference position
- Dynamic response at fixed gap
- Customer-specific acceptance rule
Common proximity probe calibration problems
No voltage reading
Check SIG, COM, and −V wiring, confirm the Prox channel is selected, and verify the driver is receiving power from the AT-2040.
Incorrect scale factor
Confirm the probe and driver are matched, the target material is correct, the micrometer position is accurate, and the linear range from the datasheet is being used.
Unstable readings
Check for loose clamps, probe misalignment, cable movement, target movement, or a probe tip that is not perpendicular to the steel target.
Agate Technology can help you set up the right AT-2040 proximity probe workflow.
Whether you need a linear probe/driver check, a dynamic AC test, or a repeatable procedure for your calibration lab, the AT-2040 and PRX-100 kit provide a practical bench setup for proximity probe verification.
