Q. Should I be calibrating my measuring instruments and if so, how?

A. Calibration, to QS-Pro, is the means of determining a resolution and origin factor for a measuring instrument where these values are not fixed and cannot simply be looked up and typed in.  Generally only analog probes, LVDTs and half bridges etc, fall into this category.  If you have a measuring tool that has a digital interface such as RS232 or Digimatic, then you will not have to calibrate it within QS-Pro.  All you need to do is type in its resolution and origin factors when you create the QS-Pro instrument.  For most modern instruments the resolution si 1 and the origin is 0.

QS-Pro instruments use their resolution and origin factors to convert raw port data into meaningful units like millimeters.  The instrument multiplies the raw data by the resolution factor, adds the origin, and the result is millimeters.  This lets QS-Pro use any type of instrument regardless of its native measuring unit - you can convert inches to millimeters or vice versa by selecting the appropriate resolution factor.

Analog probes, on the other hand, have a sensitivity that is dependent on their construction and on the gain of their signal conditioning circuit.  Neither of these values can be looked up for any given probe type and, worse, they vary slightly from one probe or interface card to the next.  Even the geometry of the gauge or fixture can have an effect.

Calibration gets around this problem by reading the raw data when the probe is measuring a setting master of accurately known size.  It does this twice and can then back-calculate when the resolution and origin values need ot be in order to read the correct size on both setting masters.  This is in fact the solution of a pair of simultaneous equations.  So, to calibrate a fixture using analog probes you will need two setting masters that have features within the measuring range of the probes and iseally near the top and bottom end of the expected range of parts being measured.  Generally one of these master will also be used as a reset master and used to reset the gaueg at regular intervals.

The recommended calibration procedure is to mount the reset master in the fixture, ensuring that all probes are touching and none are reading over-range.  Reset all the probes on this master.  Next start the calibrate function (you can calibrate all the probes at once) and 'accept' the current (ie. zero) reading.  Replace the reset master with the other master, ensure all probes are touching and none are over-range, and accept the new data.  QS-Pro will now show the readings of all the probes you jus calibrated in millimeters - or whatever units you gave for the masters.

In general you will need to calibrate a typical gauge only rarely - once every month or two perhaps or when a probe has been replaced.  but you should reset it, using the first, reset, master often, perhaps every 50 or 100 measurements, or every hour or two.