Chapter 1 Introduction CAL-BENCH Instruction Manual
1-2
Technical Assistance
If you encounter a problem with your Cal-Bench
™
system, review
the configuration information for each step of the start up and opera-
tion procedures. Verify that your settings and adjustments are con-
sistent with factory recommendations. Refer to Chapter 5, Trouble-
shooting, for specific information and recommendations.
If the problem persists after following the troubleshooting proce-
dures outlined in Chapter 5, contact Sierra Instruments, Technical
Support at (800) 866-0200 or (831) 373-0200 between 8:00 a.m.
and 5:00 p.m. PST. When calling technical support, have the fol-
lowing information on hand: the system serial number, your In-
struction Manual, flow range of the unit under test and the problem
you are encountering.
How the Cal-Bench System Operates
In operation, the calibration gas flows through the device under test
and into one of the three tubes in the Cal-Bench
™
system The tubes
are precision bore quartz borosilicate glass, each equipped with a
frictionless mercury sealed piston. The tubes are sized to provide a
ten to one ratio in volumetric displacement between the tubes.
As the gas enters the tube, the sealed piston rises. The Cal-Bench
system uses a non-intrusive, non-contact technique for measuring
the position of the piston in the tube. A specialized sonar transceiver
emits a pulse of sound energy operating at approximately 50 kHz.
This pulse of energy travels down the tube, is reflected from the top
of the piston and returns to the transceiver. The system measures
the transit time of the energy pulse, the transit time becoming shorter
as the piston rises. The computer calculates the speed of sound
based on the ambient conditions of temperature, pressure and rela-
tive humidity. By knowing the speed of sound, and the transit time
of the sonar pulse, the position of the piston can be determined with
a resolution of 0.006 inches.
To determine the mass flow rate, the Cal-Bench system uses the am-
bient conditions and converts actual volume displacement into mass
flow. The data on flow rate is displayed on the computer terminal
while the test is underway, permitting fast, real time calibration.
The Bell Prover option extends the calibration range of the standard
Cal-Bench system. The Bell Prover is essentially a larger “glass
tube” with the ability to measure higher flows. The prover is con-
structed of 300 Series stainless steel, fitted with inlet and outlet
valving, two counter weights, an optical encoder, and automated in-
puts of temperature and back pressure measurements.