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Chapter 32

Measurement and sensing

Two lessons in Part XI, Applications. Read them in order, or start anywhere: a prerequisite is a link, never a gate.

Start with 32.1
0 of 2 readabout 40 minutes

Lessons in this chapter

Two panels of the amplitude spectrum in dB re 1, from −80 to 5 dB, lower levels drawn on the floor. The panel 0 to 5 kHz: frequency in kilohertz. The panel orders: order from 0 to 8, that is 0 to 200 Hz. 0 to 5 kHz: a solid spectrum with three tall lines at 25, 50 and 75 Hz, a floor near −41.7 dB, and a hump from 2.5 to 3.5 kHz. The resonance band, 2.5 to 3.5 kHz, is shaded and labelled resonance; its median is −37.9 dB. Orders: lines at orders 1, 2 and 3, marked by dotted verticals labelled 1×, 2× and 3×, at 0.0 dB, −8.0 dB and −17.1 dB; between them the floor. A dashed vertical labelled defect at order 3.60, 90 Hz, where the spectrum reads −35.5 dB. Between 80 and 200 Hz, 6 noise bins stand taller than it.Two panels of the amplitude spectrum in dB re 1, from −80 to 5 dB, lower levels drawn on the floor. The panel 0 to 5 kHz: frequency in kilohertz. The panel orders: order from 0 to 8, that is 0 to 200 Hz. 0 to 5 kHz: a solid spectrum with three tall lines at 25, 50 and 75 Hz, a floor near −41.7 dB, and a hump from 2.5 to 3.5 kHz. The resonance band, 2.5 to 3.5 kHz, is shaded and labelled resonance; its median is −37.9 dB. Orders: lines at orders 1, 2 and 3, marked by dotted verticals labelled 1×, 2× and 3×, at 0.0 dB, −8.0 dB and −17.1 dB; between them the floor. A dashed vertical labelled defect at order 3.60, 90 Hz, where the spectrum reads −35.5 dB. Between 80 and 200 Hz, 6 noise bins stand taller than it.

Lesson 120 minYou are hereRead

Vibration and machine monitoring

Read a machine's vibration spectrum in orders of its shaft speed, then find a hidden bearing crack by band-passing, taking the envelope and its spectrum.

One panel, time from 0 to 30 s across and tilt from −40 to 45° up. The true tilt is a dashed line (true): level, up to 30° over 5 to 7 s, down to −20° over 15 to 18 s, back to 0 over 24 to 26 s. Drawn to 30 s: the accelerometer's readings, small dots (accelerometer), scatter about the truth, error 3.00° RMS since 5 s. The gyroscope's added-up angle, a solid line (gyroscope), follows the turns and is 15.2° off now.One panel, time from 0 to 30 s across and tilt from −40 to 45° up. The true tilt is a dashed line (true): level, up to 30° over 5 to 7 s, down to −20° over 15 to 18 s, back to 0 over 24 to 26 s. Drawn to 30 s: the accelerometer's readings, small dots (accelerometer), scatter about the truth, error 3.00° RMS since 5 s. The gyroscope's added-up angle, a solid line (gyroscope), follows the turns and is 15.2° off now.

Lesson 220 minYou are hereRead

Sensor signal conditioning

Sensors lie by offset, drift, noise and spikes. Fuse a noisy accelerometer and a drifting gyroscope into a steady tilt with a complementary filter.

After this chapter

Where to go next.

The chapters either side, and the rest of Part XI in the library.

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