3.0 - ER200 - IBM/Bruker ER200D scan program
|Purpose:||Basic information about the computer interface to the Bruker ER200D EPR spectrometer including hardware, software, and user instructions.|
|Date:||4 June 1992|
Not all IBM/Bruker ER200D spectrometers were created equal. There are significant revisions to the PROM chips in the ER023M module which interfere with this combination of hardware and software. Therefore, this setup does not work on all ER200D spectrometers. If you want to use this system, you should carefully check out the serial numbers of the ER023M and contact me directly. It might be wise to send me your ER023M for testing.
Spectrometer: IBM/Bruker ER200D with an ER023M signal channel and the ER023MT interface. This is the configuration sold by IBM as a computer controlled spectrometer with the IBM-9000 computer.
Computer IBM/AT compatible computer, hard disk, VGA or EGA graphics, IOTech Personal488 interface card installed and the IOTech Personal488 DOS driver loaded.
The computer's IEEE-488 card is cabled to the IEEE-488 connection on the back of the ER023M signal channel. All devices on the IEEE-488 must have an address: the address of the ER023M should be 26 ( it can be selected on the back of the unit ), the computer's IEEE-488 card is self configuring.
You must load the IEEE488 driver software on your computer before starting the ER200.EXE program. I do this in the computer's autoexec.bat file:
c:\ieee2.6\drvr488 /I /D1 /A&H02E1 /B21 /F8 /TCRLFEOI /ECRLF /SC
I have made this driver available as file ieee.zip on our Internet WWW site. This contains more files than are actually needed; probably only the drv4888.com file is actually needed.
The computer program is compiled as ER200.EXE. Copy this program to the \lab directory of the hard disk. Temporary files are stored in the \lab\eprdata directory of the hard disk. The IOTech IEEE-488 DOS driver must be loaded before ER200.EXE (see above).
The ER200.EXE program can test the computers side of the IEEE interface using the SCAN:TEST menu selection. On my system, this is the result:
File Number : 5
HELLO> Driver488 Rev 2.6 (c) Copyright 1987-1989 Iotech Inc.
STATUS> C 21 G0 L S0 E00T0 C0 P0 OK
I am not certain if this should be the result on all systems.
The spectrometer is operated normally. All experimental parameters are entered on the spectrometer, the computer controls only the starting and stopping of the scan. During the scan(s), the spectrometer recorder arm stays at the left limit of its range. After the scan(s), the recorder arm is released by the computer. Also, during the scan(s), the ER023M is in remote mode and does not respond to direct input, you cannot change signal channel parameters during a scan. Following the scan(s), the ER023M may display the REMOTE message; then press the LOC key to return the unit to local mode.
The computer program ER200.EXE works very similarly to the SCAN.EXE program described in the EPR SOFTWARE MANUAL. Important features are:
Scan speed Although the scan time can be set to a lower value, 60s is the practical limit for acquiring data across the IEEE bus to a personal computer.
Scan menu All interface features are found under the SCAN menu.
Scan time Set the scan time on the computer using the CONTROL option.
Number of scans Set the number of scans on the computer using the CONTROL option. You may select to have each scan either stored separately or averaged into one scan.
Field Center These two parameters are not acquired from the spectrometer and must be entered into the computer through the PARAMETERS option.
Time Constant These four parameters are acquired from the spectrometer at the end of a scan.
Data points The computer acquires data with a default of 2048 data points.
Interface option This menu option contains entries for the IEEE address and time constant and mod amp calibration values. They are NOT used by the program in any way.
Test option This menu option tests the programs communication with the IEEE-488 bus, not with the ER023M signal channel. If no error message occurs with this option, then the computers responsibility for the communication is OK.
Calibration The Modulation Amplitude and the Phase settings on the ER023M signal channel are not automatically calibrated values; they must be calibrated each time the unit is turned on. The calibration process is described completely in the ER023M manual that is provided with the spectrometer. Alternatively, the computer could be programmed to store the calibration values and reset the ER023M each time the unit is used; however, this program does not do this. At the LMB, we don't bother to calibrate the signal channel every time the spectrometer is used: we know that the Mod Amp setting on our ER023M is four times too high and adjust the values after the scan, and we leave the Phase at its optimum setting without adjusting that value to zero.
Signal Clipping The ER023M performs the actual Analog to Digital (A/D) conversion and, like all such units, has a finite input voltage range. The spectrometer can be tuned to an apparently good cavity match and still have a base line offset which causes spectral peaks, positive or negative, to exceed the range of the A/D converter, therefore clipping the extremes of the signal. This is particularly possible with flat cells in a TM110 cavity, and at high gain. The clipped data cannot be recovered after the scan. Three possible fixes can be applied to this situation:
- Reduce the spectrometer gain. This is a only relative value and the spectrum can be expanded in the intensity domain with the computer post scan. The primary purpose of the gain is to bring the signal into a range appropriate for the A/D converter.
- Change the ER023M offset to bring the signal away from the clipping.
- Re-tune the sample.
Now that you understand the basics, you can acquire data from the ER200 spectrometer.
- Turn on the spectrometer and the computer.
- Start the ER200.EXE program on the computer. Use the Test option to verify the communications.
- Insert the sample and tune the spectrometer. Set the spectrometer parameters and, if uncertain, find the signal on the spectrometer recorder.
- Set the computers data directory using the Directory menu option.
- Set the needed Scan time and Number of scans on the computer using the CONTROL menu option.
Select the <Begin> menu option, then confirm this choice.
The computer will now take control of the spectrometer and acquire data. Following the scan(s), you will be prompted for the spectrum filename.
- Enter the filename for spectrum storage. If you do not wish to store the spectrum, press Enter or Esc.
The spectrum will be stored as an LMB binary data file. To store the data in an ASCII format, do not use this save option; instead, escape from the SCAN menu and use the FILE menu SAVE option to store the spectrum.