Hot-Cathode Control Qualification Service
Ideally ion tubes could be calibrated and characterized by their sensitivity -- that is their "gauge factor" -- without regard to the control used to operate the tube. However the following parameters, for which the control is responsible, affect the gauge factor.
Most controls purport to provide the NIST value of the first two parameters, grid and filament bias. However, the actual values of these bias voltages may differ substantially from the specified values. Most controls allow the use of 1.00 mA for the emission current; a few controls change this current from one value to another depending on the pressure range. The filament heating voltage varies in wave form and value from control to control.
The degree to which a gauge factor measured with our NIST-certified controls will hold if the tube is operated on a different control will depend on how wildly the operating parameters vary between the two controls. By making a careful comparison of the operating control to our NIST-certified control used to establish he tube's gauge factor -- a process called "qualifying" -- the error involved can be estimated. In many cases this error is small enough to permit gauge factors measured with our NIST-certified control to be used. Qualified controls may be used with our tube calibration service to make NIST-traceable pressure measurements with substantial cost saving.
To qualify a control, a tube is first calibrated using GFV’s standard
calibration procedure as described in the Tube Calibration site. For
more information click Tube
Calibration. The
control to be qualified is then set to this gauge factor; other parameters
of the control, such as the emission current, are set as closely as
possible to the NIST standard values.
A system calibration is then performed as described in the System
Calibration site. For more information click System
Calibration.
The errors observed in the system calibration are then analyzed for the presence and quantity of systematic error. A report is prepared providing recommendations for using tubes with gauge factors certified traceable to NIST by GFV and recommendations for the maintenance of the control.
Check first with GFV to determine if the control you wish to use is qualifiable. Order "Qualification Service." Ship control to GFV; ask if we need cables and a copy of the control's instruction manual. Price: $650.00 for each control type. A complete test report is provided, including instructions for maintaining calibration. Delivery is one week from receipt of control, cable, and manual. Qualification service require one week from receipt of control.