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