Description
of System Calibration for High VacuumSystem Calibration Service
Description
of System Calibration for High VacuumA Bayard-Alpert tube and control calibrated by the National Institute of Standards and Technology (NIST), Gaithersburg, MD is used as a standard. Total calibration is accurate to ±5% as determined by NIST's accuracy and the long-term stability of the tube's gauge factor. The tube under test is attached to the test stand opposite the NIST tube. The voltages used to operate the tube are recorded. These values are monitored over the measurement cycle.
For ionization gauge controls the grid bias is measured and recorded; the filament bias is measured and recorded. Emission current is set for 1.00 mA unless emission current setting is used to establish sensitivity, see below.
For cold cathode gauge controls the applied high voltage is measured and recorded.
The system is pumped until the background pressure indication from the NIST system indicates 2x10-6 Torr or lower.
For controls which provide the feature, sensitivity is set to provide zero error at one point: the nitrogen leak is opened until the pressure rises to a NIST indication of approximately 5x10-5 Torr. The test control's sensitivity is then adjusted so that the test pressure indication Pt less the test background pressure Ptbg indication is equal to the NIST pressure indication Pn less the NIST background pressure indication Pnbg,that is
The value of sensitivity for which the test control has been set is recorded.
The nitrogen leak is closed. When the background pressures stabilize they are recorded. The leak is then gradually opened and a number of test pressure readings are recorded as the pressure is increased. The nitrogen response of the system is calculated by subtracting the background from the reading. The values are provided in the attached test report. A logarithmic plot as shown is provided. For information on interpreting the plot click interpret.
Description of System Calibration for Low Vacuum
For equipment designed to measure pressure in the range 10-4 Torr to 1000 Torr the procedure is similar to the procedure described above except that NIST-traceable capacitance gauges are used as the standards.
Order "System Calibration Service." Ship control and tubes to GFV; call to find out if we need cables or a copy of the control's instruction manual.
Hot cathode gauge calibration price: $575.00 including the first filament; additional filaments are $263.00 per filament.
Cold cathode gauge calibration price $575.00 including the first tube; additional tubes are $263.00 per tube.
Low vacuum calibration is $263.00 per tube. A single point calibration is available for $150.00.
Delivery is one week from receipt of control, tubes, cables, and manual.