Scientific Counter Single-Channel Spectrometer (SCSCS)

Contents

  1. Copyright
  2. Introduction
  3. Features
  4. Components Of Device
  5. Technical Specification
  6. Configuring the System
  7. Modes of Operation
  8. Software
    1. 1. Standard Functions
    2. 2. Higher-Level Program SCSCS

1. Copyright

Radicon LTD. Scientific Instruments
68, Malookhtinskii av., St. Petersburg, 195272, Russia
Tel.: +7(812)528-0278, Fax: +7(812)528-6633, Telex: 121590 Rebur SU

2. Introduction

Scintillation counter single-channel spectrometer is designed for energy- dispersive count rate measurements of foton flux in various types of diffraction, spectral, absorption and other experiments under control of IBM PC XT/AT compatible computer.

SCSCS consists of two blocks, connected by a cable:

  1. interface card, insertable into IBM XT extension slot, containing also micropocessor, clock, energy discriminator and sound control loudspeaker.

  2. detector block, containing scintillation crystal in assembly with beryllium entrance window, photomultiplier, high-volstage supply and preamplifier with manually adjustable gain.

This construction ensures very compact, low-consuming, inexpensive and flexible device, substituting commonly used apart-standing spectormeter units. Additional advantage is the absence of high voltage connecting cable, which significantly simplifies the installation of the detector block on the moving parts of instrumentation.

3. Features

4. Components Of Device

Standard Devices include the following components:

  1. Detector block
  2. Printed curcuit card, insertable into IBM PC compatible computer
  3. 5m long cable, connecting detector block and interface card
  4. Spare photomultiplier
  5. Spare scintillation crystal in assembly with berillium entrance window
  6. Diskette with software

The detector block includes scintillation crystal assembly, photomultiplier, high voltage source, preamplifier, scaling amplifier with manually adjustable gain, 10-position gain selection switch, 8 pin cable connector, coaxial control connector.

Printed curcuit card includes IBM AT/XT bus connector, 8 pin cable connector, 4 pin control connector, interface civuitry, 1816BE31 microprocessor (analog of Intel 8031), RAM 2 KB, ROM 512 B, clock, registers, plugin-jumper enabling switching between normal operation and testing mode with external generator, 4 bit address selection switch, two 12 bit digital to analog converters defining the pulse discrimination upper and lower thresholds, voltage converter from 5 to ~15V for feeding DACs, input amplifier, two successive filters - pulse formers, scaling amplifier, comparators of upper and lower thresholds, digital logic circuitry, forming the rectangular count pulses for microprocessor, piezo loudspeaker with control circuits.

This construction ensures very compact, low-cosuming, inexpensive and flexible device, substituting commonly used apart-standing apectrometer units. Additional advantage is the absence of high voltage connecting cable, which significantly simplifies the installation of the detector block on the moving parts of the instrumentation.

5. Technical Specification

Setting Value(s) Unit
Energy range, preset by manufacturer 5 - 25 keV
Energy range with readjustment 5 - 60 keV
Discriminator threshold range 0 - 2.56 V
Discriminator threshold resolution 2,5 mV
Exposure time adjustment 0.1 - 1000 s
Counting rate 0.1 - 10E+5 1/sec
Maximum number of counts 4 x 10E+9
Diameter of detector block mounting part 40 mm
Connector cable length 5 m

6. Configuring the System

Before installation of the printed circuit card into computer you should select and note the port addresses, used for data transfer between card and data bus of computer. If more than one card are installed in the same computer, port addresses for each card should be different. Port addresses are chosen by 4-bit switch S1 on the board. Its bits are numbered from 1 to 4. The following table gives the relation between the position of S1 switch and port addresses for data and control codes, used by the software to communicate with device.

S1.1 OFF OFF OFF OFF OFF OFF OFF OFF
S1.2 OFF OFF OFF OFF ON ON ON ON
S1.3 OFF OFF ON ON OFF OFF ON ON
S1.4 OFF ON OFF ON OFF ON OFF ON
DATA 0100H 0110H 0120H 0130H 0140H 0150H 0160H 0170H*
CONTROL 0101H 0111H 0121H 0131H 0141H 0151H 0161H 0171H*
S1.1 OFF OFF OFF OFF OFF OFF OFF
S1.2 OFF OFF OFF OFF ON ON ON
S1.3 OFF OFF ON ON OFF OFF ON
S1.4 OFF ON OFF ON OFF ON OFF
DATA 0180H 0190H 01A0H 01B0H 01C0H 01D0H 01E0H
CONTROL 0181H 0191H 01A1H 01B1H 01C1H 01D1H 01E1H

The combination marked with (*) should not be used in computer configurations with two hard disks. The combination with all S1 bits ON should never be used because of interference with first hard disk.

7. Modes of Operation

Device is capable of operation in several standard modes. There are three modes of count rate measurement: count number od pulses during preset exposure time, measure the time necessary to count the preset number of pulses, continious (cycle) count of pulse number during 65 msec intervals. The last mode is used for software emulation of intensity measurement with integration time constant T. In this case the subsequent values of intensity I(n) are calculated with the recurrence relation:

I(n) = I(n-1) * (1 - 65 msec/T) + N(n)/T
were N(n) is the number of pulses, count during the n-th 65 msec interval. The validity of this formula requires that T is much greater, than 65 msec. Intensity is measured in pulses per second.

There are also two modes of pulse amplitude discrimination: discrimination with two (upper and lower) thresholds and single (lower) thresholds discrimination, or integral mode, when all the quanta with energy exceeding the lower limit are counted.

There is also possibility to choose between the modes of operation with sound control and without it. For sound control special circuit transforms the count pulses in rectangular pulses of 1 msec width, which are fed to piezo- loudspeaker. Due to irregularities in pulse distribution specific noise is well audible even if the average count rate is about 100000 pulses per second.

8. Software

The diskette, supplied with the device, contains several object modules, performing standard functions of computer communication with the detector card. These modules are translated with Microsoft C 5.1 under MS DOS (versions 3.20 - 5.0 may be used), and should be linked with Microsoft C library for large memory model. These tools enable consumer to write his own higher-level programs to use the device in his specific system, following the description below.

There are three standard functions:

init.obj
begwrk.obj
getinf.obj
which are kept in kompot.obj file, keeping also some other internal procedures, not used by consumer directly. This file should be linked together with the higher-level program.

Below the calling of standard function is commented.

8.1. Standard Functions

init ( data_reg, control_reg )

This function loads the program for microprocessor from IBM PC. The program itself is kept in the file scscs.prg, which should be necessarily in the working directory.

Parameters:

data_reg, control_reg
integer type (2 bytes). Contain the data and control port addresses, which should correspond to the S1 switch setting on the board.

Return codes:

0
normal termination
-1
communication error (no reply from device). May be caused by improper use of port addresses or by a physical damage of device.
-2
file scscs.pgr is not found in working directory.
-3
wrong state of device. In this case press the RESET button of PC or switch computer power OFF and ON.

begwrk ( function_code, data_reg, control_reg, upper_limit, lower_limit, time, pulse_number, integral mode )

This function sets the necessary operating parameters for the device and initiates the measurement process, if necessary.

Parameters:

function_code
type integer (2 bytes). The following codes are used:

0
set the pulse count mode during preset time.
1
set the time measuring mode for preset pulse number.
2
set the continious (cycle) counting during 65 ms intervals.
3
set sound on.
4
interrupt the current job.
5
set the thresholds.
6
set sound off.
data_reg, control_reg
integer type (2 bytes). Contain the data and control port addresses, which should correspond to the S1 switch setting on the board.
upper_limit, lower_limit
integer_type (2 bytes) in the range 0 - 1023. These parameters define the discrimination threshold levels, and are used only with function code 5. Has no meaning in other modes.
time
float double type (8 bytes). Defines the exposure time in seconds. Time resolution is equal to 1 microsecond. This parameter is used with function code 0 and has no meaning in other modes.
pulse_number
unsigned long integer (4 bytes). With function code 1 this parameter presets the number of pulses to be count. Has no use in other modes.
integral_mode
integer type (2 bytes). Used with function code 5, cancels the upper threshold discrimination, when equal to 1, and restores the discrimination, when equal to 0. Has no meaning in other modes.

Return codes:

0
normal termination.
-1
communication error (no reply from device). May be caused by improper use of port addresses or by a physical damage of device.
-2
device is busy. This code is generated after attempt to change thresholds or other important parameters during the exposure time. Sound may be switched OFF and ON at any time.

getinf ( function_code, data_reg, control_reg, time_pointer, pulse_pointer )

This function ensures obtaining of results of the job, initiated by begwrk.obj.

Parameters:

function_code
type integer (2 bytes). The following codes are used:
0
get current values of time and pulse counters.
1
get counted time, as a result of job 1 of begwrk.
2
get counted pulse number, as a result of job 0 of begwrk.
3
get counted pulse number during last 65 msec period, as current result of job 2 of begwrk.
data_reg, control_reg
integer type (2 bytes). Contain the data and control port addresses, which should correspond to the S1 switch setting on the board.
time_pointer
pointer to type float double variable, ised to keep the measured time value.
pulse_pointer
pointer to type usigned long variable, used to keep the counted pulse number.

Return codes:

0
normal termination
-1
communication error (no reply from device). May be caused by improper use of port addresses or by a physical damage of device.
-2
wrong use of function or data are not ready. This code is generated when function code of getinf is not consistent with that of begwrk, or if the measurement process is not terminated and new portion of data is not ready.

8.2. Higher-Level Program SCSCS

The device, in general, is not intended for seperate use, but in some more complicated user system, containing also other devices. This makes senseless an attempt to write a seperate sophisticated higher-level program for this device, which will ignore the structure of user system. The program scscs.c, supplied with the device, should be treated as a demonstration and testing program, being at the same time an example of usage of lower-level standard functions to help the user to write his own higher-level program. At the request of a customer, the manufacturer can supply more versatile subroutiens, satisfying the specific requirements for integration of device in user system.

SCSCS runs automatically with data and control port addresses 0170H and 0171H respectively. To run the program with another port addresses, simply include them into command line. For example, to run the program with ports 0100H and 0101H type "scscs 100 101 <enter>"

In scscs program you can preset alternatively exposure time or pulse number, set the discrimination thresholds and press <enter> on the Start line to initiate measurement. The measurement process is cycled, after finishing one expose another one is initiated automatically after some small delay. The current content of time and pulse counters is displayed during the exposure. To interrupt the program and return in parameter setting mode press <SPACE> bar. Use <Y> or <N> in appropriate lines to switch sound or upper level discrimination ON and OFF.

Further information about scscs program may be obtained from the program text and comments to it.

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