The Model MCS-PCI-P essentially contains 65,535 individual counters and a DAC (digital-to-analog converter), whose output voltage is proportional to the address number of the active counter. Before the measurement starts, a counting period or "dwell time" is selected to determine how much time will be spent counting ions in each counter location before advancing to the next counter. The measurement process starts with the first counter, and the minimum DAC output voltage. At the end of the dwell time, the counting moves to the next counter and the DAC output voltage increases proportionally. This process repeats, until counting in the 65,535th counter has been completed. At that point the MCS-PCI-P has scanned through the entire DAC voltage range, and the mass spectrometer has scanned through the designated mass range. In the MCS-PCI memory, the record of counts versus counter address is stored. This digital spectrum can be displayed as the mass spectrum on the supporting computer, and saved on hard disk for further processing.

The answers to the following questions are relevant in choosing an MCS for the scanning mass spectrometer applications:

• How many channels (bins) are needed to span the mass spectrum with the desired digital resolution?
• How fast does the mass spectrometer scan, and what dwell times are needed?
• Does the maximum input counting rate specification exceed the expected counting rate by a safe margin?
• Does the DAC output provide the ability to scan the mass spectrometer?

Why is the Model 9353-P Time Digitizer also sometimes referred to as an MCS? Answer: when its digital time resolution is set to the larger values, it functions like an MCS. For example, a 13 μs digital time resolution permits the 9353-P to operate in the same way as an MCS that is set to a 13 μs dwell time.

For more detailed explanations of the MCS function, click here

The important parameters for the MCS-PCI-P and the 9353-P in MCS applications are summarized in a comparison chart; click here to locate it.