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If the gauge is adjusted considerably or if movement parts

are replaced, it will probably be impossible to re-use the

existing dial, and a new dial will have to be plotted as part of

the calibration.

2-Counter-Weighted Pointer

With this method, we begin by producing a "linear" dial. (A

dial upon which the graduations are evenly spaced). Next,

we take a "balanced" pointer and remove the half moon at

the end of the tail. By removing the half moon, the pointer is

no longer balanced because the tail end is now lighter than

the indicating (knife edge) end. This will cause the heavy

pointer tip to "sag" or read "slow" in the first half of the scale

and read "fast" in the second half of the scale, actually over-

compensating for the original non linearity condition.

To achieve the required effect, which is to flatten out the S

curve, a counterweight is added to the tail end of the pointer

to add back some of the weight that was lost when the half

moon was removed.

By adding a counterweight, also called a "poise" onto the

tail-end of the pointer gravity can be used to force the tail of

the pointer "downward", which conversely deflects the tip of

the pointer "upward". In the first half of the scale, the coun-

terweight will cause the gauge to read faster. In the second

half of the scale, the counterweight will cause the gauge to

read slower. Since the gauge was reading slow in the first

half of the scale, the faster readings caused by the counter-

weight will compensate for the non-linearity. Conversely, the

second half of the scale which was reading fast, will be

slowed by the counterweight.

In fact, because of the gravitational effect is decreased as

the pointer approaches a vertical position (due to the

decreased moment of inertia), the counterweight will cause

no effect on the pointer at mid-scale, which is always plotted

in the 12 o'clock position on the dial. This is ideal, as no

compensation is necessary at mid-scale. The counterweight

will cause the greatest effect at ? scale (9:00) and ? scale

(3:00), which is where the most compensation is required.

Properly set, the amount of compensation caused by the

counterweight will exactly offset the amount of inherent non-

linearity as shown by the "S" curve.

Notes:

1-It is important to note that the counterweight can only be

effective when the gauge is used in the vertical or near ver-

tical operating position. Gauges used in the horizontal posi-

tion will always require non-linear dials.

2-Gauges with 6" dials do not have pointers with half moon

tails. Instead, the tail end of the pointer is wider than the

indicating end. The counterbalance offset is accomplished

by trimming the tail end of the pointer until the desired coun-

terbalance effect is achieved.

The following general rules can be used to help determine

whether a gauge has a linear or non-linear dial.

Ashcroft A4A Gauges with Non-Linear Dials

-All vacuum and compound gauges

-All absolute gauges 75 psi or less

-All gauges calibrated in the horizontal position

-Some dual scale gauges

-All gauges originally equipped with "crescent moon"

pointer tail tips

Ashcroft A4A Gauges with Linear Dials

-All that are other than above

-All gauges originally equipped with counter weighted pointers

Note: When performing linearization via pointer trimming it

is important that the trimming be done carefully so as not to

remove too much material which would result in the need to

discard the pointer and start the process over.

7.0

SPECIFICATIONS, RANGES & DIMENSIONS

7.1

STANDARD SPECIFICATIONS

Unless otherwise specified all gauges are calibrated for ver-

tical mounting. If installation is other than vertical, the order

must specify mounting positions to assure proper accuracy.

A certified copy of test results, traceable to the National

Institute of Standards and Technology, is furnished with

each gauge. Standard conditions for calibration conform to

NIST Monograph 8.

Accuracy

±0.1% of span

Sensitivity

±0.01% of span

Repeatability

±0.02% of full scale

Hysteresis

Not greater than ±0.1% of span after

application of maximum scale pressure

Pressure Types

Gauge, compound, absolute* and vacuum

Pressure Ranges

From 0-15 psi through 0-100,000 psi

Bourdon Tube

Material

Bourdon tubes are available in the

following materials:

STANDARD

Beryllium Copper for ranges from 0-15

through 0-40 psi AISI 403 stainless steel

standard for range 0-50 psi through

0-100,000 psi

OPTIONAL

Beryllium Copper for ranges from 0-50

through 0-10,000 psi. AISI 403 stainless

steel for ranges 0-15 psi through 0-40 psi

Standard Process

Connections

⁄

NPT female back for ranges to 10,000

psi. 9/16-18 UNF-2B female back connec-

tions for ? inch high pressure tubing for

ranges over 10,000 psi

Optional Process

Connections

⁄

NPT female, bottom

⁄

NPT male, back or bottom

⁄

NPT male, back or bottom

⁄

NPT female, back or bottom

⁄

-18 UNF-2B female, bottom or back or

1 6

bottom for ranges below 10,000 psi

MS 33656-4 male, back or bottom

Mil-G-18997D male, back or bottom

MS 33649-4 female, back or bottom

MS 16142 female, back or bottom