May 22 – 27, 2016
Europe/Stockholm timezone

quadEM: EPICS software for digital electrometers

May 25, 2016, 12:15 PM
Medicon Village Auditorium (Lund)

Medicon Village Auditorium


Tunavägen 24 Lund


Dr Mark Rivers (University of Chicago)


quadEM supports quad electrometers/picoammeters, typically used for photodiode-based x-ray beam position monitors, or split ion chambers. They can also be used for any low-current measurement that requires high speed digital input. There is support for several models: - The AH401 series (AH401B, AH401D) and AH501 series (AH501, AH501C, AH501D) picoammeters originally designed by Synchrotron Trieste (elettra) and now sold commerically by CAENels. These devices communicate using TCP or UDP over 100 Mbit/s Ethernet or high-speed serial. They provide 4-channel current measurements at up to 6510 Hz (AH501 series) or 1000 Hz (AH401 series). - The TetrAMM picoammeter sold by CAENels. This device communicates using TCP/IP over 1 Gbit/s Ethernet. It provides 4-channel current measurements at up to 20 kHz. - The NSLS Quad Electrometer (called NSLS_EM in this document). This device consists of a 4-channel digital electrometer unit with Ethernet communication. The device provides 4-channel current measurements at up to 2500 Hz. This is now being sold commercially by Sydor Instruments. The quadEM software includes asyn drivers that provide support for the following: - Analog input records using the NDPluginStats plugin from the synApps areaDetector module. This provides digitally averaged readings of the current, sum, difference and position at speeds that are determined by the AveragingTime record described below. The quadEM drivers do the callbacks on the asynGenericPointer interface for NDArray objects required to use the areaDetector plugins. The NDPluginStats module is used to compute the averaged readings. It also provides additional statistics including standard deviation, min, max, and a histogram of values. - The NDPluginStats provide time-series of the statistics. These can be used to for on-the-fly data acquisition applications, where the meter is triggered by an external pulse source, such as one derived from a motor motion. - Streaming data to disk at the full rate from the device. This is done using the file plugins from areaDetector. - Time series data (like a digital scope) of the current, sum, difference and position at speeds up to 20000 Hz. The data is available in standard EPICS waveform records, using the NDPluginTimeSeries plugin from areaDetector/ADCore. The time per point can be greater, in which case it does averaging. - FFTs of the time series data, providing the power spectrum of each signal as another EPICS waveform record. This uses the NDPluginFFT plugin from areaDetector/ADCore. - epid (fast feedback). This provides fast feedback via an asyn D/A converter (e.g. dac128V), also at speeds up to 20000 Hz. If it is run slower it does signal averaging. This support is provided in the synApps std module. The quadEM drivers do the callbacks on the asynFloat64 interface required to use the epid fast feedback device support.

Primary author

Dr Mark Rivers (University of Chicago)

Presentation materials