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Technical Note (National Research Council of Canada. Division of Building Research), 1962-05-01
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The DBR Multipoint Pressure Recorder
Stephenson, D. G.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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No.
369NOT 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 experimental
studies of the performance of chimneys and the air leakage characteristics of buildings.
The system consists of the following components which are all 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 Corpor ation).
The recorder used with the DBR manometer system has been adapted to produce a punched paper tape record as well as the strip
chart. This modification is described in DBR Technical Note No. 351. (1)
The manometer will operate without the tape output, but having results on ｰｾＮ｣ｨ･､ paper tape allows the data proces sing to be done with a digital computer.
(1) Stephenson, D. G. D. B. R. Digital Recording System, National Research Council, Division of Building Research, Technical Note No. 351, Ottawa, November 1961.
z
-The inter connection of the various components is shown in Fig. 1. The millivolt output of the pressure transducer is directly connected to the input of the recorder measuring circuit, 1. e. the input signal does not go through the 16-point input selector switch. Instead. the recorder selector switch is used to control the Datex pressure switch which switches the pressure inputs to the transducer.
The Datex pressure switch control unit has provision for either remote or local control. In the remote mode the switch can be controlled by the recorder selector switch, but it may be switched to local mode and manually set to any point. Thus the manometer can be used either as a multipoint machine measuring and recording several inputs in sequence or as a single-point machine with the indication recorded quite frequently.
Cal. Pressure
x
Pressure
The Statham transducer uses strain gauges to measure the deflection of a diaphragm. It is compensated against changes in temperature but the output with zero pressure difference across the gauge may drift a bit. Similarly the transducer sensitivity may change with time so the system has been made self-calibrating. For two of the 16 points in the recorder cycle the pressure switch is set so that there is zero pressure difference across the transducer. The zero output is recorded at the first point; at the second a calibrating resistor is connected in parallel with one of the strain gauges and the resulting output recorded. The calibrating resistor is connected into the
bridge circuit by a relay which is closed when the recorder selector switch reaches that point in the cycle. The calibrating resistor in parallel with one arm of the strain gauge bridge gives the same output as occurs with a certain pressure difference across the gauge. The pressure equivalent of the calibrating resistor is determined when the
gauge is initially calibrated against a precision micro-manometer. It is called the calibrating pressure. The pressure corresponding to any transducer output is given by
= Output - Zero Cal. - Zero
where Cal. and Zero are the outputs of the transducer for zero pressure difference with and without the calibrating resistor connected.
The recorder can record other millivolt signals at some of the points in the recorder cycle. For example. wind speed has been recorded along with the differential pressures across building walls. The inclusion of data from sources other than the pressure transducer requires the 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
3
-16). EMF's at other points can be included by connecting them to free points on selector B and connecting the plus terminal of the same ｾｵｭ｢･ｲ･､ points on selector A to the switching relay. Selector B can
also be used to control a second pressure selector if it is necessary to switch the inputs to both sides of the pressure transducer.
FIGURE 1
BLOCK DIAGRAM OF RECORDING SYSTEM
EMF Inputs
• +
+
Paper Tape Punch 1'1 Format Control Selector B Potentiometer Recorder Selector A Press. ｴＭｾＭＭｴ Trans-ducer I' Calibrate Control Pressure Switch Control Unit Press Switch Pressure *"(- - - Inputs f----ｾ f-
,.-SELECTOR
FORMAT
PAPER TAPE OUTPUT
CONTROL FOR
SELECTOR
:I:
A
Bu
ZERO
ｾ
";J
I
+
I
+
3:
POINT
PRESSURE CALIBRATION
(/)
