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The Diagnostics screen shows important information regarding the base and cell pressure, cell temperature, and optical
sensor reading. These are continuously monitored when the base is operating.
Setting User Preferences
The CalTrak SL 800 offers enhanced electronics options to allow the user to define parameters specific to an application.
These parameters may be entered from the Operation screen or by pressing the blue section of the Measure screen.
“Sensor Factor”
As applicable, change the sensor factor from its default value of 1.000 to the value provided by the MFC or MFM
manufacturer. See Using Sensor Factors.
“PTVM”
PTV stands for Piston Tare Value, which is the amount of gas that passes around the piston during measurement. All CalTrak
calibration equipment has a factory set PTV that is stored in the memory of the CalTrak cell. The value is typically very
small: 0.008 for the ultra-low flow cells, 0.1 ccm for low flow cells, 0.2 ccm for medium flow cells, and 1.4
ccm for the high
flow cells. We adjust for this leakage by adding PTV to the measurements.
On our highest accuracy instruments, we allow for the adjustment of the Piston Tare Value with the Piston Tare Value
Multiplier
(PTVM). When using the instrument with gas species other than air or nitrogen, the molecular behaviors of these gases may
degrade the PTV. For highest accuracy, the instrument’s PTV can be adjusted. Adjusting the PTV is
accomplished by entering
a new PTVM. The PTV is multiplied by the PTVM to adjust the measurement. The default
value for air and nitrogen is
1.000. The PTVM can be set to any value from 3.000 to 0.200.
For flows above 20 ccm, a new PTVM can be calculated by using the viscosity of the gas being measured and accurate
results will be obtained. Calculate the PTVM by taking the ratio of the viscosity of nitrogen to the viscosity of the gas under
test. For example, to calibrate hydrogen, consider the following: at 0°C, the viscosity of nitrogen is 165.31 microPoise, and the
viscosity of hydrogen is 83.21 microPoise. Express these as 165.31/83.21, or 1.987, and enter 1.987 as the PTVM for this
cell.
When measuring alternate gases at flows below 20 ccm, or for absolute best accuracy, it may be necessary to perform a
dynamic leak test using the gas under test. Contact Sierra for information on this test.