´ Wojciech BLOTNICKI 1 , Józef WIORA 1 and Stanisław WALUS 1 Institute of Automatic Control, Silesian University of Technology(1) Tracer flowmeter with a conductive sensor ´ ´ ´ ´ ´ ´ ´ Abstract. This paper presents a research installation for developing flow measurements in open channel. A tracer technique is used where sodium chloride is applied as a tracer and a conductometric cell as a tracer sensor. Properties of the applied electrical measuring circuit, the ways of determining tracer transit time, flow rate and flow velocity are described. From conducted experiments, the expanded measurement uncertainty of flow rate is assessed as less then 6%. Streszczenie. W niniejszym artykule przedstawiono stanowisko laboratoryjne przeznaczone do badan nad metodami pomiaru strumienia obj ˛ etosci w kanalach otwartych. Zaprezentowano znacznikow ˛ a metod˛ e pomiaru z wykorzystaniem chlorku sodu oraz czujników konduktometrycznych jako jego detektorów. Przedstawiono równie˙ z uklad do pomiaru sygnalów z czujników konduktometrycznych, a tak˙ ze sposób wyznaczania czasu przejscia znacznika pomi ˛ edzy punktami pomiarowymi. Przeprowadzone eksperymenty pozwolily uzyskac wyniki pomiaru strumienia obj ˛ etosci z niepewnosci ˛ a na poziomie 6%. (Przepływomierz znacznikowy z czujnikiem konduktometrzycznym) Keywords: flow measurement, tracer method, flowmeter calibration Słowa kluczowe: pomiar strumienia obj ˛ etosci, metodza znacznikowa, wzorcowanie przeplwomierzy Introduction There are above one hundred methods of measuring the flow rate of a substance. Among them, a tracer method ex- ists. It is particularly useful when a channel can not be closed and when there is no way to mount a classic flowmeter such as flume [1]. The concept of the transit time method is very simple – a tracer is added to a stream and a time period of passing of the tracer between two (or more) detectors is con- trolled and then flow velocity or volumetric flow is determined. If the profile of the channel is known, volumetric flow rate can also be calculated [1, 2, 3, 4]. Any number of substances can be used as the tracer. Their physical or chemical properties allow one to detect their presence. Suitable detectors should also be applied. Optical detectors allow one to measure colouring or transparency of the medium; heat detectors – its temperature; ionizing ra- diation detectors – presence of radioactive substances; fi- nally, the conductometric detectors – change of liquid con- ductance. Furthermore, tracers should satisfy additional re- quirements such as good mixing ability with water [5]. The conductive method of the tracer flow measurement is not expensive and does not influent significantly on the nat- ural environment. This study describes a measurement cir- cuit with the flowmeter applying in the method and presents results of preliminary tests. Artificial channel In order to conduct the research on open channel flowmeters, an artificial channel has been build in the lab- oratory. A four meter length semicircular gutter was used as a channel. The gutter diameter is seventy millimetres. The channel is directly connected to and it is fed form an installa- tion dedicated to the flowmeter calibration in closed conduits (Fig. 1). Several flowmeters are mounted on the set-up. Each of them can be calibrated and used as a reference flowme- ter. The water cycle is forced by a water pump which has ten cubic meters per hour efficiency. Volumetric flow rate in the pipeline can be regulated using a precise valve which changes a flow in the shunt. There are also two tanks: the first one is a water reservoir while the second one is a cali- brated tank which is used as a volume standard during cali- bration of the flowmeters using the volumetric method. The water circulation using the build artificial channel is proceeded as follows: water is pumped by a pump from the reservoir tank through a pipeline and mounted on it flowme- ters. Next, it flows into the channel, from which flows into a small buffer tank and finally goes back to the reservoir (a sec- ond pump is used). The red arrow in Fig. 1 marks the water flow direction. Fig. 1. Schema of the laboratory set-up Water level and flow velocity in the artificial channel are correlated. If flow velocity is rising, water level in the channel is rising, too. There are three ways to stabilize the quantities. The first one: slope of the gutter can be regulated, the second one: flow velocity of the outgoing water can be changed by a gate valve, and finally the third one: volumetric flow rate in the water circuit can be regulated using a precise valve. After setting the desired flow rate, it is needed to wait until the steady state is obtained in the channel. After that, the water level and flow rate values can be read out. Measuring set-up An installation to the tracer transit time measurement has been mounted on the artificial channel. The installation consists of: • a tracer dispenser – mounted at the beginning of the channel, • a water level gauge – mounted at the tracer sensors, • a system recording tracer concentration. The most complicated part is the system for the tracer con- centration acquisition and it consist of: tracer detectors – electrochemical cells, a conductance to voltage (G/U) con- verter, a DAQ card and a computer with the LabVIEW envi- ronment (Fig. 2). The Promag 30F electromagnetic flowme- ter is also used as a reference flowmeter during the measure- ments. Concept of measurement The measuring principle is very simple: a tracer is in- jected into water and then tracer concentration changes are recorded at two or more measuring points. Transit time is ob- tained by comparing answers of the concentration detectors PRZEGL ˛ AD ELEKTROTECHNICZNY , ISSN 0033-2097, R. 89 NR 3a/20130 293