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Solid state event recorderfor rainfall measurement /Enrégistreur d'événement étatsolide pour la mesure de pluieM. TURNER a & G. P. BRUNSDON aa Institute of Hydrology , Wallingford, Oxfordshire,OX10 8BB, UKPublished online: 25 Dec 2009.

To cite this article: M. TURNER & G. P. BRUNSDON (1978) Solid state event recorder forrainfall measurement / Enrégistreur d'événement état solide pour la mesure de pluie,Hydrological Sciences Bulletin, 23:1, 143-149

To link to this article: http://dx.doi.org/10.1080/02626667809491776

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Hydrological Sciences-Bulletin-des Sciences Hydrologiques, 23,1, 3/1978

Solid state event recorder for rainfall measurement

M. T U R N E R and G. P. BRUNSDON Institute of Hydrology, Wallingford, Oxfordshire OX10 8BB, UK

Received 8 August 1977, revised 12 October 1977

Abstract. A solid state event recorder and reader suitable for use with a tipping bucket raingauge are described. The recorder is a small battery operated unit with very low power consumption, capable of recording 64, 8 bit, words. The portable reader unit is used to interrogate it.

Enregistreur d'événement état solide pour la mesure de pluie

Résumé. On décrit un enregistreur d'événement état solide et un lecteur dont on peut se servir avec un pluviomètre auget basculeur. L'enregistreur est une unité à batterie à consommation basse avec la capacité d'enrégister 64, 8 bit mots d'ordinateur. On emploie le lecteur portable pour l'interroger.

DESIGN PHILOSOPHY

Rainfall totals have long been recorded by mounting a funnel over a graduated collect­ing vessel; later the need to study the time distribution of rainfall led to the develop­ment first of autographic recorders, and then of magnetic tape recorders which counted the number of tips of a collecting bucket (or 'events') during short-time intervals. The mechanical failure of the tape transport mechanism in these devices is the most frequent cause of lost data, but the present availability of low-power solid-state stores in integrated circuit form means that the tips of a tipping bucket gauge can now be recorded electronically. Such a solid state event recorder and reader have been developed. The two basic units of the system are housed in small robust boxes designed to with­stand all weathers and are portable for use in the field. Once the recording sequence is initiated, events are counted and logged automatically. The stored data may then be displayed visually by means of a reader unit in the field, or they can be read auto­matically into a microprocessor at base.

POWER CONSUMPTION

Each unit uses low power CMOS integrated circuits powered by a rechargeable 5 V nickel cadmium battery. The event recorder consumes 40 /JA in the 'write' mode and 400 JUA in the 'read' mode. The reader has a current drain of 20 JUA while quiescent and 400 JUA when connected to the event recorder.

0303-6936/78/0300-0143802.00 © 1978 Blackwell Scientific Publications

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144 M. Turner and G. P. Brunsdon

EVENT RECORDER

The recorder is shown in Fig. 1. It measures 125 X 80 X 50 mm and is seen mounted inside the raingauge, to which it is connected. For extraction of the data it can be connected, via a 19-way plug and socket, to the reader (Fig. 2) or micropressor. The raingauge is the 'Rimco' gauge manufactured by Rauchfuss Ltd, Australia.

Figure 3 is a schematic diagram of the recorder. It operates as follows: the record­ing interval is timed by a crystal-controlled clock which can be set to intervals of 1,3,

FIG. 1. The recorder shown mounted inside the raingauge.

FIG. 2. The reader unit.

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Solid state event recorder 145

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Solid state event recorder 147

12 or 24 h. When the operator presses the 'start' button all the logic circuits are set to zero. Each tip of the raingauge bucket registers an event on the event recorder. At the end of the sampling period the information in the event counter is written into the random access memory at 'write' address location 'O'. The event counter is then auto­matically reset to zero and the 'write' address counter incremented by 1. Fig. 4 shows the pulse sequences. This process continues until the information has been fed to the memory at 'write' address location '63'. The next increment then inhibits the clock and no more information can be stored in the memory until the 'start' button is pressed again. Data are now held in store until it is overwritten with new data or destroyed by power failure.

READER UNIT

Figure 2 shows the unit housed in a waterproof box measuring 175 X 80 X 50 mm. The unit carries a 19-way connector, for plugging into the event recorder, six toggle switches, for selecting the appropriate address location, a 'read enable' switch and a 'read' push button switch. Events read into the unit from the recorder are displayed on a three-digit liquid crystal display. The unit is small and light weight for easy use in the field.

Figure 5 shows a schematic diagram of the unit. Having connected the reader to the recorder the 'read enable' switch is set to 'enable' and the required location in the store is selected by means of the toggle switches. The 'read' button is then operated and the contents of the store are indicated on the reader's liquid crystal display. All, or any one, of the 64 words can be displayed, in any desired order. Alternatively the recorder may be returned to base and read by a microprocessor.

APPLICATIONS

Although described for use with tipping bucket raingauges the equipment can be used for recording data from any sensing element which feeds out trains of pulses, e.g. anemometers. Because of its simplicity and low cost it is particularly suited for use where technical back-up is not available. With its low power consumption it can be left unattended for long periods, its battery being recharged by a small solar panel. The system's limitation is in its storage capacity of 64, 8 bit, words but this could be extended to 12 bit or 16 bit words, or to a capacity of 256, 8 bit, words where neces­sary. It could be used for such applications as recording a year's rainfall in weekly totals.

COSTS

The approximate cost of either a 64 or a 256 8 bit store is £250. A magnetic tape event recorder costs aroxr.d £750 and while its capacity is considerably greater, this would be wasted in an application of the type described here. As technology progresses, solid state stores an order of magnitude larger than those described will become available, narrowing the difference in capacities between the two systems. A further advantage

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Solid state event recorder 149

of the system described is that the data can be read on the visual reader unit, either in the field or at a base, and the cost of the reader unit is only about £200. The cost of equipment required to input the data from either a magnetic tape record or a solid state store into a computer is about the same, and is in the order of £1000 to £1500.

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