#### Gage Scan Filter

You can use the Gage Scan Filter to improve the accuracy of circular feature measurements. It corrects measured scan data by comparing it to similar scan data from a gage. This comparison reduces the amplitude of frequencies found in the measured scan data by gage amplitudes of the same frequency. This adjustment eliminates noise characteristics intrinsic to the measuring machine and probe, thereby providing more accurate measurements of the part.

The Gage Scan Filter applies only to these strategies:

- Adaptive Circle Scan Strategy

- Adaptive Cylinder Concentric Circle Scan Strategy

Enabling the Use Gage Scan Filter

1. Access the Probe Toolbox.

2. Select the Measurement Strategies tab.

3. From the list of strategies, select one of the above applicable strategies.

4. Select the Advanced tab.

5. Mark the Use Gage Scan Filter check box.

Configuring the Filter

The filter parameters are stored with the sensor tip data. You can use the single tip calibration command to associate scan data on a gauge with the active tip.

To configure the filter:

1. Measure the gage at the desired point density using a circle basic scan. If you are using a calibration sphere, be sure to carefully position the probe so that the circle scan takes place right on the equator. The gage must have a diameter close to the size of the feature on the part you want to measure using the gage scan filter.

2. Select Insert | Calibrate | Single Tip to insert a single calibrate active tip command.

3. Reference the scan in the single tip command by typing the ID into the calibrate active tip command, similar to this example:

SCN2 =BASICSCAN/CIRCLE,NUMBER OF HITS=2986,SHOW HITS=NO,SHOWALLPARAMS=YES

<-3.8456,-33.4523,0>,CutVec=0,0,1,IN

InitVec=1,0,0,DIAM=100,ANG=0,ANG=360,DEPTH=10,THICKNESS=0,PROBECOMP=YES,AVOIDANCE MOVE=NO,DISTANCE=0

FILTER/NULLFILTER,

EXEC MODE=FEATURE,USEHSSDAT=YES,USEDELAYPNTS=NO

BOUNDARY/

HITTYPE/VECTOR

NOMS MODE=MASTER

ENDSCAN

CALIBRATE ACTIVE TIP WITH FEAT_ID=SCN2

4. If desired, you can also reference both the inner and outer circle scans by adding another calibrate active tip command, like this:

CALIBRATE ACTIVE TIP WITH FEAT_ID=SCN2 (SCN2 is the inner circle scan)

CALIBRATE ACTIVE TIP WITH FEAT_ID=SCN3 (SCN3 is the outer circle scan)

Your tip data stores the gage parameters scan inside the probe file (.prb). This means that once the tip has been associated with the gage scan data, you can use the probe file in part programs where you need to measure circular features using the gage scan filter.

Improving Accuracy

For the gage that you use to determine gage filter parameters, do the following to improve accuracy:

- Choose a gage whose size is as close as possible to the size of the feature on the part.

- Place the gage as closely as possible to the location of the feature on the part. Any deviation between the two introduces a frequency proportional to the positional offset. This negatively impacts the results.

You can also improve accuracy by defining a point density (sample frequency) for the feature to measure with a value as close as possible to the point density used to measure the gage. Since the gage scan filter is applied in the frequency domain, achieving greater similarity between the gage's point density compared to the feature scan's point density results in more effective correction.