Quartz Crystal Microbalance Digital Controller

viiiOverviewExternal 10 MHz Input ConnectorThe QCM200 features a built-in frequency counter to measure the resonant frequencyand display it on the front panel. The stability and accuracy of the frequency counter ismore than adequate for most QCM experiments. For extremely demanding applications,an external timebase, such as the SRS FS725 Rubidium Frequency Standard, caneliminate all frequency errors.The external 10 MHz input allows the input of an ultra-high stability timebase signal.This input presents a 1 k input impedence and takes a 1 volt peak-to-peak (nominal)input amplitude. The BNC shield is connected to chassis ground.The QCM200 has an internal ±1.5ppm TCXO oscillator. The internal oscillator willattempt to phase-lock with a user supplied external 10 MHz signal when “T External” isselected from the front panel or the “T1” command is sent via the remote RS-232interface.The internal oscillator frequency may be “pulled” up to ±10ppm to achieve phase lock.The front panel display can indicate how far the internal oscillator is being pulled as apercentage of its full range (±100). This percentage provides a gross indication of thestability of the external 10 MHz input. After warmup of both the external oscillator andthe QCM200, a pull percentage that fluctuates by more than a couple of counts indicatesa problem with either the internal or the external oscilator. Contact SRS for assistance inthis case.QCM200 Quartz Crystal Microbalance