Patent GB-1494346-A (GB)
Title: Measuring solids in fluids
IPC: G01N15/06
Filed: 1974-11-19
Abstract: 1494346 Measuring composition of fluent materials TEKKEN KENSETU CO Ltd 19 Nov 1974 [19 Nov 1973 4 June 1974] 50022/74 Headings G 1 A and G 1N [ Also in Division E1] A method of measuring the amount of solid material entering a fluid path between a feed system and a drain system comprises: measuring at each of the feed and drain systems the density and flow of the fluid passing through the system; calculating, for each system, the amount of solid material contained in the fluid; and taking the difference between the amounts of material so calculated. Principle of Measurement In a shielded-slurry excavator wherein an aqueous slurry, which may already contain some solid matter, is pumped via a feed line into a pressure chamber of a cutter, and wherein mud, containing excavated solid matter, is pumped out via a drain line, a densimeter and a flowmeter are provided both in the feed line and in the drain line to measure, for each line, the density γ i  and flow-rate Q i  of the total material in the line. If the density of solid material in a sample of soil taken at the excavation site is γ o , then the mass rate of transfer, G i , of solid material past the measuring point, is shown to be given by the density of clean slurry being assumed to be unity. The difference between the values of G i  calculated for the feed and drain systems is the mass rate of excavation of solid material. The Densimeter: Fig. 3B A gamma-ray source 302 irradiates a flow pipe (not shown) and a reference ionization chamber 304 provided with an adjustable zero-setting attenuator 305. Radiation transmitted by material in the flow pipe, detected by a second ionization chamber 303, is compared with that detected by the reference chamber 304, the difference signal being converted to A.C. and amplified at 309, then rectified and processed at 311 to provide an output at 312 representing the density of the material. The Flowmeter: Fig. 6 An e.m.f., induced by the motion of the material across a magnetic field excited by an A.C. source 603, is detected at 601 and synchronously rectified, the output being divided by a quantity proportional to the magnetic flux density to provide at output terminals 602 a signal representing the flow-rate. Calculating Apparatus: Fig. 2 At the feed side, A, a slurry density signal γ 1 , provided by the converter 113 in response to the gamma-ray detector 106, is applied to a ratio setter 114 which calculates the quantity (γ 1 -1)γ o /γ o-1 , using a value for γ o  set into the ratio setter 114 by a potentiometer adjusted to correspond to a measurement on a soil sample. The ratio setter 114 output is combined in a multiplication/division computer 116 with a flow signal Q 1 , derived by the converter 115 in response to the flowmeter 107, to give an output representing the mass flow-rate of solids through the feed system A. Similar apparatus at the drain side B provides a signal representing the mass flow-rate of solids through the drain system. An addition/subtraction computer 121 provides a signal representing the mass excavation rate of solids to an indicator 122, a recorder 123, an integrating recorder 124 and a counter 125. The Excavator: Fig. 7 A rotary cutter head 202 is driven in a slurryshield type excavator body 201 enclosing a pressure chamber 204 which communicates with a slurry feed pipe 206 and a drain pipe 207 of larger diameter than the feed pipe, each pipe containing a densimeter 208 (209) and a flowmeter 210 (211). A first drain pipe section 218 feeds the slurry into a separator 212 containing a trommel 213 from which larger particles can be extracted via a drain port 214 while the remainder is exhausted by a second drain pipe section 216. A feedback pipe 217 allows liquid slurry to be pumped back to an injection port 219 at the mouth of the first drain pipe section 218 so as to wash out any heavy particles and to smooth the slurry with the help of an agitator 220. A pressure alarm device 225 gives warning if the trommel 213 becomes clogged. A detector 223 sensing the pressure in the chamber 204 controls a valve in a feed by-pass 224. If the soil has a significant amount of large particles that would be extracted by the trommel 213, the measuring apparatus may be disposed in the first drain pipe section 218. The measurement may be used to control the advance of the cutter in step with the rate of excavation, to avoid collapse of the tunnel.