A low cost data-logging system

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A low cost data-logging system Johnson, G. L.; Jones, G. L.

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by ANALYZED'

G.L. Johnson and

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A LOW COST DATA-LOGGING SYSTEM

by

G.L. Johnson and L. Jones

ANALYZED INTRODUCTION

An energy monitoring study was carried out recently in a l o c a l

public school to determine:

(1) electricity-consumption patterns for a typical classroom area (mainly l i g h t i n g ) , f o r portable classrooms [lighting and heating),

and f o r HVAC equipment; and

(2) service hot-water consumption and efficiency of t h e service w a t e ~ - h e a t ing system (reported in Ref. 1)

.

Measurements of electricity consumption, temperature and flow (oil and water) were required a t 30-min intervals.

This Note describes and evaluates the s y s t e m used to collect

these data.

DESCRIPTION OF MONITORING SYSTEM

The system was required to meet t h e following criteria:

(1) measure k i l o w a t t hours, flow rates and temperature;

(2) run f o r one month without a t t e n t i o n ;

(3) store data in a form convenient for subsequent processing;

(4) provide a wide range of sampling intervals; ( 5 ) operate without f a i l u r e ;

( 6 ) cost s i g n i f i c a n t l y l e s s t h a n equipment o f similar capability;

( 7 ) be easily installed and serviced; (8) be accurate to tl% or better.

A suit able commercially available data- logger, which invariably had many more channels than were r e q u i r e d , would have c o s t approximately

$ 5 , 0 0 0 ; magnetic tape data storage would have increased t h i s to $11,000.

system. The system xequirements were met by incorporating:

(1) visual readout counters that respond to contact closures from

kilowatt-hour and flow-meter outputs;

(2) a cine-camera to record these readings and provide a permanent data storage medium;

(3) commercially available equipment such as t i m e ~ s , counters, and

cameras, to meet the requirements of reliability and low

case.

DESCRIPTION OF EQUIPMENT

A complete l i s t of the equipment used i n t h i s project, and i t s

cost, is contained in Table I . All of the components are "off the s h e l f i i terns.

Transducers

Figure 1 outlines the basic system c o n f i g u r a t i o n . The f r o n t - e n d

transducers c o n s i s t of t h e f o l l o w i n g :

(1) thermocouples attached t o hot- and cold-water pipes;

(2) flow meters, factory equipped with contact-closure o u t p u t s t o allow

remote reading of accumulated flow, installed in oil and water

l i n e s ;

(3) kilowatt-hour meters, factory equipped with contact-closure

outputs to allow remote reading of accumulated energy consumption, installed in selected electrical circuits.

Monitoring Panel

The remote readout indicators were grouped together on a display

panel (Figure 2).

(1) S i x 120

V

for various equipment, (only two were used Sn t h i s _{study to indicate} burner and circulating pump operation).

(2) A 12 V DC gas-discharge d i g i t a l display clock with am/pm indication was provided as an independent and secure time reference,

(33 Two l i g h t - e m i t t i n g - d i o d e (L.E.D.) thermocouple indicators were installed to provide readout of temperatures.

(4) Seven L.E.D. s i x - d i g i t counters were installed to provide readout

from contact-closure type tra~lsducers. Each counter had a factory-installed standby b a t t e r y t o r e t a i n the count in t h e event of an interruption of power.

( 5 ) The f r o n t of the display panel was painted f l a t black to minimize reflections. The panel was completely enclosed for safety. Two power inputs were provided to t h e panel: 120 V mains AC for readout and

counter operation, and 1 2 V DC, provided by an automotive battery, for t h e clock.

Cameras

Two Super 8, low-light cine-cameras were used with 160 ASA f i l m

to r e c o r d t h e panel readings. A remote-control facility on the camera allowed the exposure of one frame at a t i m e . A commercially available programmable timer was used to t r i g g e r the camera a t intervals as s h o r t

as 5 min.(See Figure 3 . ) The normal 6 V DC battery supply contained

in t h e camera handle, required t o power t h e camera, was replaced by two external 6 V lantern batteries to provide longer operation.

The decision to use a cine-camera i n preference to a video tape

recorder or _{35 mm still camera was based solely on cost. The Super 8} provides 3600 frames in a standard 50-ft c a r t r i d g e and, therefore, has

the c a p a b i l i t y of storing a large amount of data at low c o s t .

SYSTEM EVALUATION

'Ihe over-all system performed satisfactorily during the seven

months of operation. Only two loss-of-data incidents occurred. One of these was due to low battery power to the light meter circuitry, which

was corrected by more frequent replacement of batteries; t h e o t h e r involved

a j ammed camera, which operated satisfactorily after r e p a i r s were made.

Film readability was excellent. Occasionally t h e r e was some difficulty in distinguishing a particular d i g i t in a number (between 8 ' s

and 3 ' s for instance, or if a digit was in the process of changing when

t h e frame was exposed). This could usually be resolved by advancing or

backing up one frame on the film to determine the preceeding and sub- sequent readings. The L . E . D . and gas-discharge displays performed well, and registered very well on f i l m . The film t a k e n of the utility-supplied kilowatt-hour meter, however, was unsatisfactory because of poor film

image and low meter resolution, which made interpretation o f t h e meter reading d i f f i c u l t .

To avoid this problem and to eliminate t h e need for an additional camera t o photograph the utilities meter, it is recommended that

arrangements be made with the electric utility to allow a connection from the utility meter to the display panel.

The monitoring system proved to be very suitable for r e c o r d i n g

accumulated data, such as flow or kilowatt-hour consumption readings,

a c a p a b i l i t y that was n o t a v a i l a b l e as a standard feature an commercial data-logging equipment. It was not as good for measuring such things

on f i l m . One solution to t h i s is t o increase the frequency of recording and average these readings when processing t h e data.

It is felt t h a t t h e present system could b e expanded to handle about 20 readout displays. F o r more c h a n n e l s , t h e camera-ta-panel distance would need to be increased, o r t h e zoom lens adjusted to increase thc f t e l d

o f view w i t h a resultant decrease in the s i z e of the counter images on t h e

f i l m .

Self-illuminated d i s p l a y s are much better than non-illuminated d i s - plays. Where e x i s t i n g meters with non-illuminated displays musr b e p l ~ o t o - graphed it is recommended that a close-up l e n s attachment be used, and that

g l a r e - f r e e lighting of the meter face be provided. In order to maintain

a time reference, i f none is available within the field of view, an electric m i s t w a t c h can be mounted an t h e meter glass.

DATA PROCESSING

Processing of the film by a high-quality photographic laboratory is rccomended. Specks on t h e processed f i l m because of poor processing procedures can cause loss of data on s frame; splices can cause the loss of a number of hours o f data.

In the current work, the processed film was viewed through a standard cine viewer-editor; data from each frame was transferred through a mini-computer to a data base on flopgy-disc. Programs were m i t t e n to organize this data storage and to carry out various computations. The

average time taken to read the film, type the numbers into the computer, process the data, and list input and output information worked o u t t o be

l e s s than 2 min f o r a film frame containing nine & d i g i t numbers.

A low-cost data monitoring system utilizing a cine-camera has

been developed. The system has proved to be reliable over i t s seven month operation and i s considered particularly s u i t a b l e for measuring

accumulated-type data such as kilowatt-hours and, with limitations, for

recording output f r o m existing meters.

REFERENCE

I , L. Jones. Hot Water Consumption and Performance of an Automatic

Storage Type Service Water Heating Installation in a School Building.

TABLE I SCHEDULE OF EQUIPMENT USED

Approximate c o s t per u n i t

[I978 prices)

TRANSDUCERS

Canadian General Electric - c o s t dependent upon type of meter; equipped w i t h D - 5 1 pulse generator (1) Kilowatt -hour meters [3 phase) (23 Water-f law meters

Neptune green seal w i t h Model 34 impulse switch (3) Oil-flow

meter

Kent Mini-major with pulse output

(43 Kilowatt-hour

meter boxes

Canadian Electric Box

- c o s t dependent upon meter

DISPLAY PANEL

(I) Cameras Sankyo ES44XL or ES66XL

electronic system camera (2) Tripod

(3) Timer

(43 Temperature

indicators

Therms-electric ELPH digital themnocouple indicators

(2 @ $260)

(5) Counters Veeder Root Electronic Totalizers with panel mount and standby battery [7 @ $170)

(63 Clock D i g i t a l , with WJPM indication -Heathki t

(7) Panel Construction: 8 h @ $25/h

8 h @ $12Jh

T o t a l c o s t o f d i s p l a y p a n e l $2516

OTHER

Batteries ( 6 V lantern type)

Film,

EKT

SN

Processing of film ( I ) Operational

HOT WATER SUPPLY

HOT lQATER REWRN

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MOM4 TORlNG PANEL COMSlSTl NG OF L. E. a. DISPLAY COUNTERS FOR

CONTACT-CLOSURE IMPIJTS.

DfG l Tdl THERMOCOUPLF READOUTS FOR

TEMPERATURES, CLOCK FOR

Tlk!E REERENCE. AND NEON ON/ OFF INDICATORS

a FFFI) FROM - n n h l l l J L L I I I L I \

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DISTR IBUTION EQUIPMENT FEEDS TO PORTABLE CLASSROOMS

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Figure 2 Monitoring panel

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