Understanding Auto Range & Auto Gain Range

The P8000 Auto Range and the Auto Gain Range functions are often confused by users. They are not the same, but they are related.

Auto Gain Range Button

The Auto Gain Range is a function that will select the best gain automatically. In order to use it the P8000 should be armed and have sensors connected and working.

The user should then perform a practice test, that means the noise or vibration should be measured as though the test was running. All the time the P8000 should be armed.

When the Auto Gain Range button is clicked, the software will look at what the input levels have been whilst the system was armed and the practice test completed. The system will select the best gain based on the requested Percentage Full Scale (%FS) that is desired. The auto gain range function will try to make the signal’s maximum level reach the desired %FS. In Figure 1 we can see the %FS set to 50%.

Auto Gain Range button
Figure 1: Auto Gain Range button

For example, assume we have a signal that has a range of ±2.5 volts. With a gain of 1 the ADC has a range of ±10 volts. So our signal uses 25% of the maximum range.

We have selected a %FS of 50% so when the Auto Gain Range button is clicked, the system will choose a gain of 2. The full range will then be ±5 volts and so our ±2.5 volt signal will use 50% of the available range.

Note that the Auto Gain calculation can only go up, not down. If clipping occurs the gains will be reset to 1 on clicking the Auto Gain Range function.

Auto Range column in the setup matrix

The Auto-Range column in the DATS Acquisition setup matrix (see Figure 2) is used to select which channels are effected by the Auto Gain Range button as described above. The values in this column can be set to either Yes or No. When the Auto Gain Range button is clicked and the value is set to Yes, the auto range calculations will be applied to that channel. When set to No, the gain setting of that particular channel will not be adjusted.

Auto-Range column in the setup matrix
Figure 2: Auto-Range column in the setup matrix

 

 

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James Wren

Application Engineer & Sales Manager at Prosig
James Wren is an Application Engineer and the Sales Manager for Prosig Limited. James graduated from Portsmouth University in 2001, with a Masters degree in Electronic Engineering. He is a Chartered Engineer and a registered Eur Ing. He has been involved with motorsport from a very early age with special interest in data acquisition. James is a founder member of the Dalmeny Racing team.

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