Technical Comparison: 100 mV/g vs. 50 mV/g Accelerometers

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INTRODUCTION
There are several differences between accelerometers with 100 mV/g sensitivity and those with 50 mV/g sensitivity. The current standard sensitivity in the condition monitoring industry is 100 mV/g. This was not always the case - 50 mV/g was the industry-standard sensitivity before 100 mV/g replaced it.

Previously, 50 mV/g accelerometers were utilized as a standard in the condition monitoring industry for two reasons:
▶ Sensor technology limited 100 mV/g accelerometers to a dynamic range of ±50 g regardless of the readout instrumentation to which it was connected
▶ Readout devices (the predecessor to modern analyzers) were limited to a ±5 V full-scale range, which limited a 100 mV/g accelerometer to 50 g’s of vibration range (100 mV/g x 50 g = 5 V)

Taking these limitations into consideration, users of this technology in the past would achieve a wider dynamic range of 100 g’s using a 50 mV/g accelerometer (50 mV/g x 100 g = 5 V) when compared to a 100 mV/g accelerometer.

As technology has improved, industry standards have changed and we can compare modern sensor technology when utilized with the auto-scale capability of modern data analyzers. The following comparison of 100 mV/g vs. 50 mV/g sensitivity accelerometers will use CTC’s AC102 (100 mV/g) and AC117 (50 mV/g) accelerometers. Use the following links to view the technical datasheets for AC102 and AC117 which will be referenced for this comparison:
AC102 Datasheet
AC117 Datasheet

These sensors have identical dimensions and weights, making them ideal for this comparison.

FREQUENCY RESPONSE
One of the primary characteristics when comparing an accelerometer is the frequency response range that each accelerometer is capable of accurately measuring. Each accelerometer has a standard sensitivity (100 mV/g or 50 mV/g) with a published tolerance to which it will generate an output to the stated sensitivity.

The above chart helps to understand which speeds each accelerometer sensitivity is effective at detecting. In both cases for a lower frequency and for a higher frequency, the 100 mV/g sensitivity is superior to the 50 mV/g sensitivity. To further specify, the AC102 (100 mV/g) accelerometer allows you to detect frequencies from 0.5 Hz - 1 Hz and 12,500 Hz - 15,000 Hz within a tolerance of ±3 dB which is not a capability with the AC117 (50 mV/g) accelerometer.

DYNAMIC RANGE
The next characteristic we are going to look at is the dynamic range of each accelerometer. The dynamic range is characteristic of the transducer that allows the electronic amplifier to pass signals from a given amount of vibration.

If we reflect on the earlier topic of legacy readout devices having a ±5 V full-scale range limit and combine this limitation with the  ±80 g, peak dynamic range of the AC102, the user would experience signal clipping. However, with modern technology and the ability of auto-scaling through digital signal analyzers, the user will not experience signal clipping when utilizing a sensor like the AC102 that has a  ±80 g, peak dynamic range.

SPECTRAL NOISE
The last difference between both sensor technologies is spectral noise. This characteristic only affects the signal of the sensor at extremely low speeds. In a real-world setting, the user is likely to never face issues from spectral noise from either 100 mV/g or 50 mV/g accelerometers. However, for our comparison, we will adventure into the differences.

In conclusion, CTC’s modern 100 mV/g accelerometer technology with a ±80 g dynamic range allows the user to identify bearing faults at slower and higher speeds when utilized with modern analyzers. This helps users predict bearing failure in earlier stages when compared to past users utilizing 50 mV/g sensor technology with legacy readout devices.