Tuesday, January 4, 2011

On Nested Polynomials

At work we use quartz pressure gauges to measure downhole pressure in a reservoir. The gauges are extremely accurate and employ a clever temperature correction scheme. They are calibrated at a test facility somewhere in the States and sent to us as a kit. The calibrations take the form of nested polynomials, the coefficients of which have to be entered manually into an acquisition system. Apparently computers prefer crunching this form of equation to the regular type. Here is what they look like (more or less).

So just figuring

  • 25 Coefficients per internal gauge 
  • 3 Internal Gauges
  • 4 Coefficients per external gauge
  • 29 Coefficients per Internal/External Combination
  • 9 Possible configurations means 261 coefficients to enter (manually) into the system.
The possibility of typos is tremendous. Luckily the system allows some test values to be input so as to generate a known output. Its fairly easy to check if you've made a mistake. Still its a lot of typing for the two-fingered. Once all the calibrations are entered then the gauges must be phsically checked (in their various combinations ) just to ensure all the points are entered in the right places. Lots of unscrewing and screwing involved here.

This will take all day...I'm already pooped.

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