Nuclear Instruments and Methods 216 (1983) 161-164 161

North-Holland Publishing Company

A CAMAC DATARATE SUPERVISION M O D U L E

J.C. W I K N E

Institute of Physics, University of Oslo, Blindern, Oslo 3, Norway

Received 23 December 1982 and in revised form 11 April 1983

A CAMAC module that monitors the data flow rate in a CAMAC crate is described. The module can, independently of the computer, generate an audible or visual alarm as response to a detected rate that falls outside a preset window.

1. Introduction

In the use of computer based data acquisition equipment for nuclear experiments the need often arises to continuously monitor the data flow rate, since a change in this rate may indicate changing experimental conditions or malfunction in the apparatus.

Especially in cases of long experimental runs it is highly desirable to make the flow surveillance automatic, in a sense that the experimentator 's attention is attracted if a flow rate outside a preset "window" is detected.

A method of doing this, using commercially available equipment, is to apply one or more scalers as rate counter(s), and to have a computer routine that compares the scaler data to predefined values. If a mismatch is detected, an alarm may be generated through a suitable output facility of the computer.

Such an approach, however, for one thing dedicates a (probably costly) general purpose scaler to a task in which its resolution as well as other possible facilities are hardly needed. Moreover, erratic flow rates due to malfunctions in the acquisition system itself, such as software errors or computer downs, may fail to be detected.

The present paper describes a simple and inexpensive alternative in the shape of a single-width CAMAC [1] module, hereafter called the Dual Channel Datarate Supervision Module (or Dual Channel Datarate Alarm).

The module has been used in several experiments at the Oslo Cyclotron Laboratory.

2. Functional description

The Datarate Supervision Module is built around two 8-bit frequency counters, of which one, Channel 1, has its TTL-compatible input permanently hardwired to the CAMAC strobe $2 to monitor the activity on the dataway itself, while the input of the other, Channel 2, is available for counting other events through a LEMO contact on the front.

The time base is common for both channels. The front panel features, besides the Channel 2 input, a LEMO socket for an external alarm, controls

for upper and lower rate thresholds and individual alarm enable switches for each channel, status indicators and a time base select switch.

The enabling/disabling of the unit and the data register readout are done through CAMAC. The NAF commands implemented are:

F(0)A(0) Read Rate Register 1 (Channel 1).

F(0)A(1) Read Rate Register 2 (Channel 2).

0167-5087/83/0000-0000/$03.00 © 1983 North-Holland

162 J.C. Wikne / CAMAC Datarate Supervision Module

F(8)A(0) Test LAM (Q = LAM).

F(10)A(0) Clear LAM.

F(24)A(0) Disable LAM.

F(26)A(0) Enable LAM.

The module gives LAM and alarm as response to datarates outside the preset levels. An alarm means that an on-board piezoelectric beeper is sounded, and the relay contacts connected to the external alarm output are closed.

The alarm status remains on until the rate again falls within the preset window, or the module is disabled through CAMAC or by the front panel switches. The LAM is internally latched.

If A1 and A2 are the internal alarm states of the two channels, SW1 and SW2 are the states of the enable switches, the parameter LEN means LAM enabled, and I and N true means the corresponding CAMAC lines true, then the LAM status is given by the following Boolean equation:

L A M = I . N ! . k E N . ( A l l ' . S W l + A 2 1 " . S W 2 ) . (1)

The alarm status is the same as the LAM status, except it does not depend on N, and is not latched. The 16-bit output word from the unit as read by the F(0) commands consists of three fields, a 4-bit

status field, a 4-bit time base field and an 8-bit data field as follows:

Bit: 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

$3 $2 S 1 SO T3 T2 T 1 TO D7 D6 D5 D4 D3 D2 D 1 DO

Status field Timebase field Data field

The meaning of the S and T fields is given as follows:

SO Channel 1 upper level exceeded S1 Channel 1 lower level exceeded $2 Channel 2 upper level exceeded $3 Channel 2 lower level exceeded

T3 T2 TI TO Timebase

0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0

10 ms 100 ms

l s 10s

100 s

3. Electronic description

The block diagram of the instrument is shown in fig. 1. In reading this figure, it should be noted that chips in the TTL family are listed without the "74" prefix.

The working principles are as follows: When a Time Base cycle is complete, the data from the two 8-bit Counters, 74ES393, one for each

channel, are clocked into the registers of the Data Latch and Output Buffer block, two 74ALS576, as well as into the registers of two monolithic D / A converters with storage, AD558, one for each Comparator block in fig. 1.

The D / A conversion is done to facilitate the comparing of the data to thresholds set by simple, easy-to-use 15 turn trimmer pots adjusted from the front of the module.

The actual comparing is done by the dual sense amplifier 75207, of which one half is dedicated to the

J.C. Wikne / CA MAC Datarate Supervision Module 163

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o

_a

Q. Z T Z - k - tu

g~ . . i h .

o

l ?

Fig. 1. Dual channel data-rate alarm.

STATUS DISPLAY

't U . .

z l

..a "r

z uJ I--

Ix ._1 ~

STATUS I DATA LATCH & OUTPUT BUFFER [ OUTPUT BUFFER

LS244 2xALS576

CAMAC

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upper threshold, the other half to the lower. The input sensitivity of this circuit is 10 mV, and the outputs are directly TTL compatible.

The outputs of each Comparator, "uppe r level exceeded" and "lower level exceeded", are combined by O R functions in the LAM and Control Logic block to make the parameters A1 and A2 of eq. (1).

In addition to acting according to eq. (1), the LAM and Control Logic provides the required Q-response, as well as an indication of A1 and A2 on the module front, in that it drives tri-state ( red-off -green) LEDs which change from green to red as A1 and A2 become true. The LEDs are part of the block denoted as Status Display.

The on-board alarm beeper is driven from the LAM and Control Logic through one contact set of a small print relay, whose other contact set is used for the external alarm.

The Time Base block consists of a CMOS real-time five decade counter, the MC14534, driven by a simple CMOS RC-oscillator, and a minimum of additional logic, mainly for setting the time base and deriving the correct clock pulses for the Counters and Comparators. The current time base is indicated by LEDs in the Status Display.

Decoding of the NAF commands is achieved by means of a single PROM, TBP28S42, which together with one half of a 74LS244 octal tri-state driver, and one fourth of a 7409 gate, constitutes the NAF Decoder block.

164 J.C. Wikne / CAMAC Datarate Supervision Module

As one will see, the module has been designed using three different IC technologies, as the Counter, CAMAC Output Buffer, LAM and Control Logic and NAF Decoder blocks are in TTL, the Time Base block mainly in CMOS, and most of the Comparator circuits are analog.

The circuitry of the unit totals up to only 25 integrated circuits plus a few other components, put together on a double-sided circuit board.

4. Performance

The prototype module was built in April 1982 and tested with very satisfactory results. It has since then proved its convenience in various nuclear experiments, especially during continuous 24

hour runs with few personnel in the lab at night. The versatile time base ranging through the five decades from 10 ms to 100 s has been of great

importance in coping with rates that may vary from nearly 10 kHz in singles acquisition down to 0.1 Hz in some coincidence experiments. The only restriction imposed on the data rates within these limits comes from the fact that the timebase is set manually, so rate deviations considered as normal must not exceed the span given by 8 bits.

The reason for using front panel controls for the time base and thresholds instead of making these parameters programmable through CAMAC, was partly the assumption that for most experiments it will be required to set them only once or twice during a run, partly the desire to make the unit as uncomplicated and failsafe as possible. Here it is worth noticing that a power transient may alter the contents of, or even reset, an electronic register, while a potentiometer can be considered as "nonvolatile" storage, an important fact since the unit is expected to respond to incorrect data rates that may follow an interruption of CAMAC power.

The Channel 2 input may, for instance, be used for the Event Ready line in the data acquisition system at the Oslo Cyclotron Lab [2-4]. In multiparameter experiments the number of transitions to true on this line is equal to the number of valid events registered. If D1 is the Channel 1 datarate and D2 the Channel 2 rate, then the mean event multiplicity will be directly given by:

M = D I / D 2 . (2)

Software, written in NODAL [5], has been made to supply the experimentalist with a statistic overview of the rates and multiplicity, apart from supporting the module's more obvious alarm features. FORTRAN versions of some of the software are presently being incorporated into the data acquisition program system SHIVA [6].

5. Concluding remarks

The Datarate Supervision Module has turned out to be a suitable solution to the rate monitoring problem whenever the normal variation of the rate does not exceed the span given by 8 bits, a condition that is usually fulfilled in the experiments done at our lab, and that is believed to apply to several other applications as well.

Where this condition is not met, a version with a more sophisticated, self-adjusting time base is feasible. Detailed circuit diagrams and circuit-board layout can be obtained on request to the author.

References

[1] CAMAC: A modular instrumentation system for data handling, EUR 4100e (1972). [2] G. Midttun, F. Ingebretsen and P.J. Johnsen, Nucl. Instr. and Meth. 159 (1979) 567. [3] G. Midttun, K. Holt, F. Ingebretsen and B. Skaali, A general A D C - C A M A C interface module, Inst. of Physics, Univ. of Oslo,

Report 82-10. [4] G. Midttun, F. lngebretsen and B. Skaali, A 15-fold ADC scanner for nuclear physics experiments, Preliminary Report. [5] B. Skaali, The SINTRAN III NODAL system, Inst. of Physics, Univ. of Oslo, Report 80-17. [6] B. Skaali, A. Haugem F. Ingebretsen and G. Midttun, A multi-task nuclear data acquisition system for ND-10/100 computers, to

be published.