The probe spacer affects the performance of the intensity probe. Intensity measurements are based on the phase difference between the two probes, thus the spacer length affects both to the frequency range and dynamic capability of the instrument.
The probe spacer affects the performance of the intensity probe. Intensity measurements are based on the phase difference between the two probes, thus the spacer length affects both to the frequency range and dynamic capability of the instrument.
For the Nor1290 probe, the 12 mm spacer is recommended for measurements from 31.5 Hz to 10 kHz. This is possible due to the phase calibration capabilities of the Nor145 combined with the Nor1294 Phase Calibration Coupler.
If the dynamic capability is not sufficient after phase calibration, changing to a longer spacer might be an option. For each doubling of spacer length, a 3 dB increase in dynamic capability is expected. However, the upper frequency range is limited.
In general, the lower frequency limits depend on the need for dynamic capability performance. For the upper frequency limit, the following table is useful:
| Spacer | fmax |
|---|---|
| 6 mm | 10 kHz |
| 12 mm | 10 kHz1 |
| 25 mm | 2.5 kHz |
| 50 mm | 1.25 kHz |
| 100 mm | 630 Hz |
1 Valid for the Nor1290 probe with corrections enabled.