Firing Conditions

The following information applies to the : CAL3K-AP , CAL3K-A , CAL3K-U, CAL3K-F.


The firing conditions are contained in the DEFAULT parameters and operating MODES if applicable. In general terms the firing conditions are fixed by the factory in the default settings. Only the CAL3K-A and CAL3K-AP have an "EXPERIMENTAL" mode which allows the free settings. In all other machines and modes the setting can be changed to your liking but they will return to the DEFAULT settings after a power up or abort.

Following is an explanation of the firing conditions :

INITIAL TIME (absolute, not after Drift)

The default value is 3.0 minutes. The minimum is 1.6 minutes. This is the time it takes for the vessel stability to settle down after the filling operation. Depending on the laboratory requirements and on the time restrains, 3 minutes is a good average and a RSD of 0.05% can be achieved.

INITIAL TIME (after Drift)

This time starts when the drift criteria is satisfied. In this mode 0.5 to 1.0 minutes are sufficient.

INITIAL DRIFT

The initial drift is the difference between two temperature readings six seconds apart. It is the temperature gradient or the first derivative. The second derivative (The difference between two drift readings) is called the stability.

The vessel is ‘unstable’ after filling with oxygen. Of course, all the other temperature factors play a role as well: Handling, cooling, preparation, Draft in the room, etc. If the vessel ‘leaks’ then the drift is more negative. The typical initial drift behaviour can be observed in the PC if one graphs the drift in real time.

At present a 0.015 drift gives a good overall performance.

TIME AFTER DRIFT

This is a SYSTEM DEFINITION. It can only be changed from the PC. The default setting is: OFF

In the ‘OFF’ mode both the drift and the time run concurrent. Both must be satisfied for the vessel to fire. A change in the setting affects the INITIAL TIME and INITIAL DRIFT.

INITIAL ATC OFFSET

This is the temperature gradient (offset) between the vessel and its surroundings (ATC). A +2C gradient is recommended in the DYNAMIC mode. Why not ‘ZERO’? If one plots the drift after filling then it becomes apparent that the comparisons become difficult. So the +2C is a good compromise: It assures positive drift without ‘heating’ the vessel too much. A change in the initial ATC setting affects both Initial time and drift.

CONCLUSION

At the present time the default settings are sufficient: they give good results. Of course they can be changed. The challenge is a high production environment where time and accuracy counts. Digital Data Systems is committed to constant development and improvement and we will update you with all improvements if you so wish.


READ DRIFT & STABILITY

The ‘READ’ Keyboard commands are ‘non-influential’, they just monitor in real time a particular condition. The DRIFT displays the temperature changes every 6 seconds. A negative sign indicates that the vessel temperature decreases. The STABILITY is the ABSOLUTE difference to the drift changes (It is the second’s derivative of the temperature).

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OPERATING MODES

The most popular mode is DYNAMIC because it is fast and accurate. Like all modes it is controlled by the default settings. The default settings were optimized in the factory tests and are somewhat optimal (but not perfect!). The settings in each mode can be changed via the PC interface. However, at the next: RESET, ABORT, POWER UP.

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CALIBRATION MANAGEMENT

The CAL3K Vessel has 7 chassis/mode fields and each field can hold up to 10 calibrations. If more calibrations are performed then the oldest is overridden and replaced with the latest. These 10 fields are used with the AVERAGING of calibrations. The amount of calibrations used for averaging is contained in: CALIBRATION AVERAGE

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