1. INTRODUCTION
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© 2007 DH Instruments, a Fluke Company
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1.1
OVERVIEW
The FPG8601 (Force-Balanced Piston Gauge), VLPC (Very Low Pressure Controller) and FPG Tools
(PC Based Software) are used in conjunction to act as a high precision pressure measurement and data
acquisition system. Operator interaction with the FPG/VLPC and its extensive capabilities is accomplished
through the PC based software from a computer via a standard RS232 port. FPG Tools also provides
features to define a test sequence, read DUT’s with a standard RS232 or IEEE-488 output, and log data
to a data file.
FPG pressure is defined by using a high precision load cell to measure the force exerted on the effective
area of a piston-cylinder (see Section 2). Instead of rotating the piston like other piston gauges, the FPG
provides sensitivity between the piston and cylinder by maintaining a constant flow through the annular
gap. This flow generates a centering force that prevents the piston from touching the cylinder during
normal operation. Noise normally associated with rotation is therefore not present.
FPG platforms are designed to maximize metrological performance and ease of operation in both gauge
and absolute modes. Many features are included to enhance the fundamental precision and stability of
pressure measurements as well as simplifying use and reducing the operator influence on the
measurements.
The VLPC generates low pressure in gauge and absolute modes (0 to 15 kPa). It is used to set and
stabilize pressure as read by the FPG so that the VLPC/FPG combination can be used to set user
specified target pressure values. The general operating principle of the VLPC is to generate a stable flow
through one of a number of restrictions depending on the range of pressure to be controlled (see Section
3.4). The pressure drop across the restriction is the controlled differential pressure. Feedback from the
FPG is used to dynamically readjust the flow to obtain the desired target pressure.
FPG Tools is the complete interface to both the FPG and the VLPC. An interface to all functional aspects
of both instruments is provided by the software. FPG Tools uses three basic modes of operation to
remotely interact with the FPG and VLPC:
[Run Mode]
,
[Run w/Point Logging],
and
[Run Test Sequence]
(see Section 6.5). These modes respectively allow simple monitoring of pressure, monitoring of pressure
with user dependant steps and data acquisition, and monitoring with defined test steps and data acquisition.
A DUT can be used in any run mode for real-time error determination and/or data acquisition.
