Edwards APGX-H, Instruction Manual, Page: 8 / 32

D023-92-880 Issue F
Page 2 © Edwards Limited 2018. All rights reserved.
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Introduction
as accessories. A gauge identification signal is available on the electrical connector: this signal is used by Edwards
AGCs and TICs to identify which type of gauge is connected.
The APGX-H is available in four tube options with different fittings for connection to your vacuum system: An
1
/
8
inch
NPT male threaded connection is available in stainless steel, an NW25 flange is available in stainless steel or an NW16
flange is available in either stainless steel or aluminium.
A sintered phosphor-bronze filter is fitted to the end of the gauge to reduce the affects of contamination and
turbulence in the vacuum system when pumped down or vented to atmospheric pressure.
The APGX-H contains two patented temperature sensing devices. The APGX-H uses these devices to compensate the
output for the effects of changes in ambient temperature.
Two push button switches are situated on the top cover of the APGX-H (see Figure 5 ). The switch labelled '
CAL
' is
used for setting the atmospheric and vacuum reading. The switch labelled ' SET TRIP ' allows you to change the
operating pressure of the set-point device.
The set-point output device is an open collector transistor. If you use an Edwards AGC, TIC or AGD, the APGX-H set-
point is not used.
Inside each gauge tube is a device to store calibration information. Every time the ' CAL ' switch is pressed to adjust
the vacuum or atmosphere pressure readings, the new calibration information is downloaded into the tube. If the
tube is inserted into a different electronics housing, the new calibration information will be used automatically.
1.3 Gas dependency
The rate of heat transfer through a gas is dependent upon the pressure, and the RMM (relative molecular mass) of
the gas. Therefore, the output signal of the APGX-H is also gas dependent.
The output signal voltage to pressure conversions equation applies for nitrogen and dry air, but can also be used when
you measure the pressure of gasses which have a similar RMM, such as oxygen and carbon monoxide.
Generally:

With gasses which have a lower RMM than nitrogen, the pressure indicated by the APGX-H will be higher than
the actual gas pressure

With gasses which have a higher RMM than nitrogen, the pressure indicated by the APGX-H will be lower than
the actual gas pressure
Detailed tables of voltage output as a function of pressure are available on request; contact your supplier or Edwards.