Ref: 0046/035046 - Rail Head Depth Gauge - Calibration Procedure TDS – Issue 2 February 2018

Calibration Procedure

Rail Head Depth Gauge: PADS reference 0046/035046

Prior to Calibration:

The accuracy of the Rail Head Depth Gauge is checked against a calibration fixture PADS reference 0046/035047.

1) The surfaces of the fixture should be cleaned with a dry lint free cloth.

2) Before calibration, each gauge to be checked should also be cleaned with a lint free cloth.

Prior to calibration, the general condition of the gauge should be assessed. Reject

immediately:

a) If the locking screw on the rear of the gauge is missing.

b) The vertical arm does not move freely along the full range of the engraved scale.

*Note this may be due to an ingress of dirt, which can be removed by applying a

spray type lubricant for example WD40.

General Condition:

The Rail Head Depth Gauge comprises an engraved vertical scale with a sliding

contact arm. The accuracy of the gauge is determined by the relationship of four

datum positions (a, b, c, & d) and the horizontal datum line (e) in the viewing

window. The engraved scale position is relative to those datum positions and not

from a single datum edge.

As the engraved scale is ‘fixed’ and not subject to wear, the accuracy of the gauge

can be easily and quickly assessed by verifying the collective alignment of all the

datum positions at just one engraved line position (20mm).

The fixture has been designed as a simple ‘GO’ type gauge. No measurements are

necessary. Provided that the horizontal datum line (e) aligns to within +/-0.25mm

of the at 20mm position on the engraved line, the gauge is deemed as being

within specified limits of tolerance.

Overview

Four datum positions.

Horizontal datum line (e)

aligned to 20mm position.

e

Calibration Procedure:

1) Position the gauge so that datum points a, b, and c contact with the profile of the fixture (photograph 1).

2) Lower the vertical arm so that the underside (d) contacts the top face of the fixture and tighten the locking

screw (photograph 2).

3) Check that the horizontal datum line (e) aligns with the 20mm engraved line position to within a tolerance of

+/- 0.25mm (photograph 3).

d a

c

b

Ref: 0046/035046 - Rail Head Depth Gauge - Calibration Procedure TDS – Issue 2 February 2018

Page 2

Photograph 1 Description of Procedure

Ensure each of the datum points, a, b and c contact the calibration fixture

profile as shown.

Photograph 2 Description of Procedure

Lower the sliding arm until the underside face (d) contacts with the top surface

of the fixture.

Photograph 2A Description of Procedure

The fixture can either be used on a flat surface such as a worktop, but is also of

a size that it can be held in the hand.

Photograph 3 Description of Procedure

Check that the horizontal datum line aligns to the 20mm position on the

engraved scale to with +/- 0.25mm.

Note:

The calibration fixture is supplied with a calibration certificate traceable to UKAS national standards. Provided

that the fixture is both handled and stored with care, it should only be necessary to recalibrate it every 5 years.

The calibration fixture can be returned for recalibration or can be recalibrated by any calibration laboratory. A

calibration drawing is available, our reference LAW191CAL.

a

b

c

e

d