With Quadrupole Mass Spectrometers and Magnetic-Sector/Electrostatic-Sector Mass Spectrometers, the ion rates are typically low, and the ions are simply counted for a period of time at each mass setting of the spectrometer. To record the entire mass spectrum, the electrostatic and/or magnetic field of the spectrometer must be scanned through the relevant range. The Model MCS-PCI-P can perform both the scanning and the counting function to record the complete spectrum. The diagram below shows a typical system configuration.

Instrumentation for acquiring a scanned spectrum from a quadrupole mass spectrometer by counting the detector output pulses in the MCS-PCI, as the spectrometer is scanned by the ramp output of the MCS-PCI. This scheme also works for scanning Ion-Trap mass spectrometers and magnetic-sector/electrostatic-sector mass spectrometers.

The 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.

This type of data acquisition electronics is called a multi-channel scaler (MCS). "Scaler" is a rather antique synonym for "counter", and "multi-channel" refers to the large number of counters stacked in sequence.

The Model VT120A-P Preamplifier in is used to prepare the signal amplitude for the MCS-PCI input, and the Model 556-P HV Bias Supply provides the tightly controlled bias voltage for the Channeltron^®, electron multiplier, or microchannel-plate detector.