r

DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

'fE C1HlIi ][CAlL NOTJE

No.

369

NOT FOR PUBLICATION FOR INTERNAL USE

PREPARED BY

PREPARED FOR

D. G. Stephenson CHECKED BY

Record Purposes

APPROVED By NBH

DATE May 1962

SUBJECT THE DBR MULTIPOINT PRESSURE RECORDER

This note describes how a standard multipoint potentiometer-type recorder has been converted into a multipoint recording manometer.An instrument of this type has been used extensively in experimentalstudies of the performance of chimneys and the air leakage characteristicsof buildings.

The system consists of the following components which areall available commercially:

(1) A 16-point potentiometer-type recorder (Leeds and Northrup).(2) A differential pressure transducer (Statham).(3) A l2-point pressure switch and associated control unit

(Datex Corporation).

The recorder used with the DBR manometer system has beenadapted to produce a punched paper tape record as well as the stripchart. This modification is described in DBR Technical Note No. 351. (1)The manometer will operate without the tape output, but having resultson p~.ched paper tape allows the data proces sing to be done with adigital computer.

(1) Stephenson, D. G. D. B. R. Digital Recording System, NationalResearch Council, Division of Building Research, TechnicalNote No. 351, Ottawa, November 1961.

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The inter connection of the various components is shown inFig. 1. The millivolt output of the pressure transducer is directlyconnected to the input of the recorder measuring circuit, 1. e. theinput signal does not go through the 16-point input selector switch.Instead. the recorder selector switch is used to control the Datexpressure switch which switches the pressure inputs to the transducer.

The Datex pressure switch control unit has provision foreither remote or local control. In the remote mode the switch can becontrolled by the recorder selector switch, but it may be switched tolocal mode and manually set to any point. Thus the manometer canbe used either as a multipoint machine measuring and recordingseveral inputs in sequence or as a single-point machine with theindication recorded quite frequently.

Cal. PressurexPressure

The Statham transducer uses strain gauges to measure thedeflection of a diaphragm. It is compensated against changes intemperature but the output with zero pressure difference across thegauge may drift a bit. Similarly the transducer sensitivity may changewith time so the system has been made self-calibrating. For two ofthe 16 points in the recorder cycle the pressure switch is set so thatthere is zero pressure difference across the transducer. The zerooutput is recorded at the first point; at the second a calibrating resistoris connected in parallel with one of the strain gauges and the resultingoutput recorded. The calibrating resistor is connected into thebridge circuit by a relay which is closed when the recorder selectorswitch reaches that point in the cycle. The calibrating resistor inparallel with one arm of the strain gauge bridge gives the same outputas occurs with a certain pressure difference across the gauge. Thepressure equivalent of the calibrating resistor is determined when thegauge is initially calibrated against a precision micro-manometer. Itis called the calibrating pressure. The pressure corresponding to anytransducer output is given by

= Output - ZeroCal. - Zero

where Cal. and Zero are the outputs of the transducer for zero pressuredifference with and without the calibrating resistor connected.

The recorder can record other millivolt signals at some ofthe points in the recorder cycle. For example. wind speed has beenrecorded along with the differential pressures across building walls. Theinclusion of data from sources other than the pressure transducer requiresthe use of a relay switching arrangement such as the one shown in Fig. Z.In this example two EMF's are included with the pressures (at points 8 and

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16). EMF's at other points can be included by connecting them to freepoints on selector B and connecting the plus terminal of the same~umbered points on selector A to the switching relay. Selector B canalso be used to control a second pressure selector if it is necessaryto switch the inputs to both sides of the pressure transducer.

FIGURE 1

BLOCK DIAGRAM OF RECORDING SYSTEM

EMF Inputs

• + +PaperTapePunch

1'1

FormatControl

Selector B

PotentiometerRecorder

Selector A

Press.t-~--t Trans-

ducer

I'

CalibrateControl

Pressure SwitchControl Unit

PressSwitch

Pressure*"(--- Inputsf----~

f--

,.-SELECTOR

FORMAT CONTROL FORPAPER TAPE OUTPUT SELECTOR

:I:A B

uZERO~

";J I + I +3: POINT PRESSURE CALIBRATION(/) 2 ~ RELAY + 2 +l.LI "I 3 + + 3 +a: --I 4 + + 4 +::> E.M.E FROM(/) -I 5 + + 5 +(/) PRESSUREl.LI .. I 6 + TRANSDUCER + 6 +a: 7 + 7 + 1-Q.

~...

8 +, ~ 8 1"-0~ -I 9 + 9 +

.. I 10 +. SWITCHING + 10 T(/) RELAY E.M.F.z -I II + + II +0

~I 12 + + 12 + INPUTS~ I /U ... 1 13 + /N.C. /N.C. + 13 +l.LI jl4 + + 14 +zz 15 I I0 + + 15 + tu 16 ~ 16 ,.----COMMON .1

fPOWER TOOPERATERELAYS t

TO RECORDERMEASURI NG CIRCUIT

FIGURE 2

WIRING DIAGRAM FOR RECORDING MANOMETER WITHOTHER E.M.F. INPUTS