How can I adjust the gain of the mass spec ion detectors (MCPs)?
The gain of the MCPs can easily be adjusted. The gain is defined by the voltage differential between the front and the back of the detector, which can be found on the control box as “V-DF – V-DB” and “V+DF – V+DB”. Adjust the value by adjusting the voltage to the detector, V-D and V+D, respectively. Higher voltage differential means higher gain. So much for the easy part. Now it gets trickier: adjusting the voltage to the detector also changes the potential of the flight tube and the first reflectron plate. This means that by changing the detector gain, the balance of the voltages is disturbed and the other voltages (source plates, reflectrons) have to be adjusted as well to keep spectrum intensity and resolution at a maximum. The best way to do that is by running a sample with constant composition and high hit rate, like the standard metal solution. Zoom in on a peak in a spectrum and adjust the voltages until the peak looks good. Now zoom out and make sure intensities and quality of
