MEASURING CONDUCTIVITY OF A SUSPENSION

Abstract: Since it is easier to make an accurate measurement of a volume of fluid than of a quantity of powdered material, a mixture of powdered material and fluid of desired proportions is made by weighing a container before and after adding a quantity of powdered material to ascertain the weight of the added powdered material by difference, calculating the quantity of liquid to be added to that weighed amount of powdered material and adding the required amount of fluid to the powdered material. A conductivity measurement is then made on the mixture, stirred as necessary, and once the conductivity measurement has become constant, it is compared with a standard and the contents of the container are then fed to a main analyser if the comparison is within a given tolerance or otherwise to a drain.

Description: MEASURING CONDUCTIVITY OF A SUSPENSION In conductivity measurements of a mixture of a liquid - and powdered material, it has been usual to add a fixed quantity of powdered material to a fixed quantity of 5 liquid in a container, mix the two together and make the conductivity measurement. The supply of a fixed quantity of powdered material is difficult to achieve with great accuracy, which limits the accuracy of the conductivity measurement. 10 The present invention proposes to add a quantity of powdered material to a container and to obtain an accurate weight reading of the material added by the difference of readings of the container with its contents before and after the addition and then to calculate the 15 amount of liquid required to be added to the measured weight of powdered material and to add the calculated quantity of liquid to the container and then to carry out the conductivity measurement. This arrangement has the advantage that the amount of 20 liquid added to the container corresponds accurately to the amount of powdered material in the container and is not dependent on the accuracy of delivery of a given -* weight of material to the container. The source of error in delivering material to the container is thus 25 avoided. An example of the invention will now be described with reference to the accompanying drawings in which : Figure 1 is a schematic side elevation of conductivity measuring apparatus and Figure 2 is a diagram of connections of the apparatus of Figure 1 with a microprocessor. A strain gauge 12 has a measuring head 31 supporting an aluminium seating disc 32. Supported on the disc 32 is a polypropylene vessel 11 of 250 ml capacity. A powder fill funnel 17 has a closeable outlet 33 for feeding material into the vessel 11. A fluid supply 16 extends into the top of the container 11 and is formed with a spray outlet. A 24 volt d.c. electric motor 14 drives a stirrer bl ' ade 13 at the base of the container 11 at about 1000 r.p. . by means of a gearbox 15 and a bearing housing 34- A sensor probe 27 extends into the container 11 to measure the electrical conductivity of the container contents. An extract conduit 21 extends from the base of the container 11 to a 24 volt peristaltic pump 22 leading to an analyzer conduit 23 and a drain conduit 24, each conduit being controlled by a respective pinch valve 25 and 26. A microprocessor, indicated diagrammatically in Figure 2, controls the sequence of operation of the apparatus illustrated in Figure 1. The microprocessor receives inputs from the strain gauge 12 and the output of the conductivity sensor 27- When the empty container 11 is placed on the strain gauge, a reading of its weight is fed into the microprocessor. The valved outlet 33 of the funnel 11 is opened to supply a quantity of powder material to the container and then closed again and a second reading of the container weight is supplied by the strain gauge 12 to the microprocessor. The difference of the two readings corresponds to the weight of the powder material fed into the container 11 and the microprocessor calculates from a predetermined formula the quantity of fluid to be added to the powdered material through the conduit 16 from a supply of heated liquid through a pinch valve 3 . The microprocessor receives conductivity readings from the sensor 27 and compares each reading with preceding reading to determine when the output becomes constant. The constant reading is compared with a standard in the microprocessor. If the comparison is within a certain tolerance, the pump 22 is energized and the pinch valve 25 is opened to transfer the contents of the container 11 to the analyzer along conduit 23- If the comparison indicates that the reading is not within the allowed tolerance, the contents of the container 11 are fed to the drain conduit 24 by energizing the pump 22 and opening the pinch valve 26. The container 11 is prepared for further analysis by rincing with a solvent from the conduit 16 and draining the rinsing solvent through the conduit 21, pump 22 and conduit 24- The microprocessor has a liquid crystal display 37 to indicate the readings made and the various stages of the operation. The devices for performing the various steps in the conductivity measurement illustrated in Figure 1 are by way of example only, and could be replaced by components of similar function.

Claims: C L A I M S : 1. A method of measuring the conductivity of a mixture of a liquid and powdered material comprising weighing a container, adding a quantity of powdered material to the container, weighing the container again to ascertain the weight of the added material, calculating from a predetermined formula the amount liquid required to be added to the ascertained weight of added material, adding the calculated amount of liquid to the container and mixing it with the powdered material and measuring the conductivity of the mixture. 2. A method as claimed in Claim 1 comprising repeatedly measuring the conductivity of the mixture and when the measurements have become constant comparing the constant measurement with a standard, and transferring the contents of the container to an analyzer or to a drain according to the comparison. 3. A method as claimed in Claim 1 or Claim 2 comprising adding the calculated amount of liquid to the container through a spray outlet to facilitate mixing with the powdered material.

Inventors: KAY JOSEPH BRIAN, KAY, JOSEPH, BRIAN
Applicants: MICROSPAN PROCESS CONTROLS
Application year: 1986
Main classification: G01N27
IPC codes: G01N27, G01N33