Measuring with a probe extension is really convenient when probing in hard-to-reach spaces. However, using probe extensions also increases system uncertainty. Part of this increase in uncertainty is due to the deflection of the probe.
Indeed, when applying a side force at the end of the probe, the probe bends and the center of sphere is deflected.
Let’s take a look at the beam deflection formula:
- W = Force applied
- L = Length of the stem
- E = Modulus of elasticity (Young’s Modulus)
- I = Moment of inertia
From this formula, we note that the shorter the probe and the smaller the force applied at the end of it, the slighter the deflection will be. Since the length is cubed in the equation, it is recommended to always use the shorter probe possible.
However, if you cannot measure with a smaller probe, your only option is to minimize the force applied at the tip of the probe. A good technique is to hold the probe very lightly with one hand and put pressure on the ball with the second hand (instead of applying the pressure with the probe).
Since the calibration of the probe is the first step to a good project, minimizing the deflection of the probe during this step is particularly important. When performing the calibration, hold the probe as lightly as possible. Securing the probe in the calibration cone with you second hand may also help get better calibration results.