air flow ta2_range

8/2/2019 AIR FLOW Ta2_range

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3.4,

3.5.3.6.

3.7

3.8.

Instruments in the TA-2 rangeare very easy to operate. Beforeusing the instrument, usersshould thoroughly familiarisethemselves with its features.

3.1. Three position slide switch:Up -velocity.centre -off.down -temperature.Always switch off when not in use.

3.2. Electronic zero wheel.3.3. Mechanical meter zero. With the

instrument switched off, zerothe meter by using the screw onthe meter face to adjust thepointer. This should notnormally require resetting.

Battery cover. This slides and'snaps in' at the rear undersideof the instrument case.Velocity scale in metres persecond and feet per minute.Temperature scale in degreesC and FGreen light. Flashes when unitis switched to either velocity ortemperature.Amber light. Comes onmomentarily only at switch on tovelocity mode whilst velocitythermistor is heating tooperating temperature. If this Ilight comes on at any othertime, this indicates incorrect useor a faulty instrument.

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Red light. Comes on momentarilyat switch on. If this light comeson at any other time, whilst theinstrument is in use, a lowbattery condition is indicated(see section 2).Telescopic probe and cable.The probe comprises seventelescopic tubes giving anextended length of over 900mm. With the coiled cable fullyextended, the maximum reachfrom the instrument case isapproximately 2 metres.Compensating and temperaturemeasuring thermistor.

3.5mm dia. jacksocket.

Connection is + tocentre pin. Output impedanceshould not be less than 1Ok ohms.

probe and cable.

from any air movement. Select'velocity' mode on the slide switch,alloV'J a minimum of 10 seconds forthe thermistor to warm up and thenslowly turn the zero wheel to adjustthe pointer on the scale. For greateraccuracy, the meter should be zeroedin still air at the same temperature asthat to be measured. Extend thetelescopic probe by pulling gently on

I the end cap. Ensure that the cableI can slide freely into the handle end of

the probe. It is only necessary toI extend the probe to a sufficient length

for the readings to be taken. AfterII zeroing, remove the zeroing cap. If the

probe head is to be out of sight whenI a reading is taken (e.g. insideI ducting), align the direction indicatorIon the end of the probe with theI probe head slot. The direction of airiow must be as shown by the

arrowhead on the end of the probe.

Offer the probe head into thei airstream, pointing the slot in theI direction of flow, and read the velocity! indicated. Check zero and re-zero if

necessary before each set ofreadings.Using the instrumentBefore using the instrument,

check the battery state (seesection 2 and 3.9).To measure velocity.Before using the instrument,zero electronically. Ensure thatthe zeroing cap is on the probehead covering the velocitythermistor to isolate it

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4.3.To measure temperature.Select temperature mode onthe slide switch. Place probehead in the airstream and readthe temperature indicated.

Note 1. To use a probe inside ducting,a 14mm. (0.55 in.) minimum hole isrequired in the duct wall.Note 2. If a duct traverse is required itmay help to use the joints betweenthe telescopic tubes as markers sothat the probe head position can beeasily determined.Note 3. When closing down thetelescopic probe, allow the cable toslide freely through the probe.4.4. Use of the output.

The voltage output isproportional to the meter

deflection when the instrument isbeing used in either velocity ortemperature mode. The output ISNOT directly proportional tomeasured velocity ortemperature. The velocity/ voltageand temperature/voltagerelationship is best showngraphically. See 4.4.1 to 4.4.4below. These graphs show typicalvelocity/output relationships at 20degrees C (68 degrees F).If the TA-2 instrument is used invelocity mode with the outputfeeding into a logging or recordingdevice over longer periods, duringwhich time the temperature mayvary significantly at the probe tip,accuracy may be impaired.

4.4.1. Velocity/voltage relationship -T A2-2 and T A2-4h.

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4.4.4. Temperature/voltage relationship -all TA2 models.

32 40 50 60 70 T emperature oF -T A-2-4h/T A-2-3k/T A-2-6k80 90 100 110 120 130 140 150 160 1701.00.90.8

J!}.a>Q)0)~~:50.:5O

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0.2 1/~.1

1/'00 10 20 30 40 50 60

Temperature C -TA-2-2/TA-2-15/TA-2-30 70 80

(cont) To maintain optimumaccuracy it is best to re zero theinstrument (see section 4.2), atregular intervals.This procedure is NOTnecessary when logging orrecording temperature only.

5.2.

gives the average velocity.It should be noted that quitelarge variations may be observedbetween individual readings. Ingeneral, the larger the numberof readings taken, the moreaccurate the result will be.Use of grilles.Avoid intrusion of the arm andhand into the face area of thegrille. The blockage effectcreated would cause artificiallyhigh velocity over the remainderof the grille, leading to incorrectreadings.The telescopic probe is useful inavoiding this problem.Volume flow rate calculations.

Where to use theinstrumentChecking the air velocity overlarge areas.When checking air velocity overlarge areas, a number ofreadings must be taken, spacedto give an even coverage of thewhole area.The average of these readings 5.3,

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Volume flow rate throughairways may be calculated if thecross-sectional area of theairstream and its average velocityare known.To calculate volume flow rate,the cross-sectional area of theairway is multiplied by theaverage airstream velocity,using the same units of linearmeasurement throughout thecalculation.

6.

twice the diagonal measurementof the grille. The duct should bepositioned over the grille andsealed to the wall with adhesivetape. Measurements of flow cannow be conducted at theunobstructed end of the test duct.Use of the cross-sectional area ofthe duct, not the grille, for thecalculations.

7. RecalibrationIf an instruments calibrationbecomes suspect, it should bereturned to Airflow forrecalibration to original standards.It is, in any case, good practice tohave the instrument checked atleast once a year .In the U.K., Airflow VentilationSupplies (AVS) operates aninstrument hire service for theconvenience of customershaving their instruments repairedor racalibrated. To use this facility,contact AVS, telephone (0494)463490, facsimile (0494) 471507,to make arrangements prior toreturning your instrument.

Possible sources of errorTaking a series of readings ofvelocity and averaging themmay ignore the effect of reducedvelocity at duct walls. A moreprecise method is shown in B.S.1042 Section 2.1 -LogTchebycheff method. Thismethod is recommended for usein ducts and at unobstructedapertures. Significant errors mayoccur if the aperture is coveredby a grille. The airstream issuingfrom a grille may be verydisturbed with many small areasof high velocity interspersedwith areas of low velocity. Formaximum accuracy, it isadvisable to make up a shortlength of test ducting which isjust larger than the overalldimensions of the grille. Thisduct can be made from anyconvenient rigid material andshould have a length about

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. SpecificationParameter Model Metric Imperial

TA-2-2/4h

ndicating meter 1 mA taut band0-1 volt proportional to meterdeflection, on velocity ortemperature scale

all modelsimensions of instrument 185 mm x 92 mm 7.25 in. x 3.62 in.x 30 mm x 1.25 in.

all models 194 mm.930 mm.13mm.450 gms.ll models

7.6 in.36.6 in.0.52 in.instrument only

all models 4 type M cells, alkaline, standardor re-chargeable

all models Approx. 30 hours using alkalinebatteries. Approx. 15 hours usingstandard batteries.

QUALITY ASSURED TO ISO 9001

air flow ta2_range

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