quadEM

This page is the home of quadEM.

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 two models:

1. The AH401B picoammeter designed and sold by Synchrotron Trieste (elettra). It is also sold by CAENels. This device communicates using TCP/IP over 100 Mbit/s Ethernet or high-speed serial. It provides 4-channel current measurements at up to 1000 Hz.
2. The Quad Electrometer built by Steve Ross from the APS (called APS_EM in this document). This device consists of a 4-channel digital electrometer unit and 2 VME boards. The device provides 2 readings per diode at up to 813 Hz.

Both of these units are based on the same principle of an op-amp run as a current amplifier with a large feedback capacitor, and a high resolution ADC.

The quadEM software includes asyn drivers and an SNL program that provide support for the following:

• Analog input records using the standard asynInt32Average device support. This provides digitally averaged readings of the current, sum, difference and position at speeds up to 10 Hz with standard EPICS scan times. One could also use the standard asynInt32 device support with ai records and scan=I/O Intr, in which case the record would update with every reading from the device. This is likely to overwhelm the EPICS IOC if the electrometer is run at very fast integration times.
• Time series data (like a digital scope) of the current, sum, difference and position at speeds up to 1000 Hz (AH401B) or 813 Hz (APS_EM). The data is available in standard EPICS waveform records, using the drvFastSweep asyn driver from the synApps "mca" module. 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.
• epid (fast feedback). This provides fast feedback via an asyn D/A converter (e.g. dac128V) at speeds up to 1000Hz or 813Hz. 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 epics fast feedback device support.

Please email any comments and bug reports to Mark Rivers who is responsible for coordinating development and releases.

Where to find it

You can download the software from the links in the table below:

Required Modules

The quadEM support typically uses the synApps modules mca (for digital scope mode), std (for the EPID fast feedback support), and ipUnidig for interrupt support .  But the quadEM module does not actually depend on these other modules to be built.

Installation and Building

After obtaining a copy of the distribution, it must be installed and built for use at your site. These steps only need to be performed once for the site (unless versions of the module running under different releases of EPICS and/or the other required modules are needed).

1. Create an installation directory for the module, usually this will end with
   
   .../support/
   
2. Place the distribution file in this directory. Then issue the commands (Unix style)

   gunzip quadEMRX-Y.tar.gz
   
   tar xvf quadEMRX-Y.tar
   

   where X-Y is the release.
3. This creates a <top> application.
   

   .../support/quadEMRX-Y
   

4. Edit the config[ure]/RELEASE file and set the paths to your installation of EPICS base and to your versions of other required modules.
5. Run gnumake in the top level directory and check for any compilation errors.
6. Please email Mark Rivers so that a record can be kept of which sites are using this software.

In Use

This software was originally developed by Mark Rivers.

• ANL/APS : In use at CARS and a number of other beamlines.