US-12624980-B2 - Streaming current monitor

US12624980B2US 12624980 B2US12624980 B2US 12624980B2US-12624980-B2

Abstract

A streaming current monitor comprises a cylinder in fluid communication with a flow-path between an inlet and outlet and a piston received in the cylinder. A drive mechanism is configured to drive reciprocation of the piston in the cylinder to move colloid into and out of the cylinder via an annular space between the piston and cylinder. A pair of electrodes are exposed in a wall of the cylinder and spaced apart in a moving direction of the piston to sense a charge characteristic of the colloid. The drive mechanism is a linear actuator comprising a stationary part and a moving part connected to the piston via a shaft.

Inventors

Daniel Bryan Laird Edney
Grant Anthony Bowring

Assignees

DBG IP LIMITED

Dates

Publication Date: 20260512
Application Date: 20250829

Claims (20)

1 . A streaming current monitor (SCM) comprising: an inlet and an outlet to receive and deliver a flow of colloid to and from the SCM; a cylinder in fluid communication with a flow-path between the inlet and outlet, and a piston received in the cylinder to reciprocate therein, a drive mechanism to drive reciprocation of the piston in the cylinder to move colloid into and out of the cylinder via an annular space between the piston and cylinder, a pair of electrodes exposed in a wall of the cylinder and spaced apart in a moving direction of the piston, and a shaft extending between the piston and the drive mechanism, wherein the drive mechanism is a linear actuator comprising a stationary part comprising at least one wire coil and a moving part comprising at least one permanent magnet, the at least one permanent magnet connected to the shaft, the moving part, shaft and piston together forming a moving assembly, the at least one coil configured to generate a magnetic force to drive reciprocation of the moving assembly.
2 . The SCM as claimed in claim 1 , wherein the stationary part comprises two wire coils spaced apart in a moving direction of the moving part, a first coil primarily interacts with a north end of the permanent magnet and a second coil primarily interacts with a south end of the permanent magnet.
3 . The SCM as claimed in claim 1 , wherein the SCM comprises at least one magnetic position sensor to provide an indication of a position of the permanent magnet of the moving part of the linear actuator, the at least one position sensor located at an axial centre region of the permanent magnet.
4 . The SCM as claimed in claim 3 , wherein the at least one position sensor comprises a pair of position sensors spaced apart in a moving direction of the permanent magnet, and a controller configured to determine the position of the moving part independent of a variation in a magnetization of the permanent magnet based on output from the pair of position sensors.
5 . The SCM as claimed in claim 1 , wherein the shaft is removably connected to the moving part of the actuator, so that the shaft and piston is removable from the SCM without removing the permanent magnet from the linear actuator.
6 . The SCM as claimed in claim 1 , wherein the SCM comprises a pair of bearings supporting the shaft, the pair of bearings located between the moving part and the piston.
7 . The SCM as claimed in claim 6 , wherein the bearings are arranged towards opposed ends of the shaft.
8 . The SCM as claimed in claim 6 , wherein the shaft is many times longer than the piston.
9 . The SCM as claimed in claim 6 , wherein the pair of bearing comprises a piston end bearing and a drive end bearing, and wherein the cylinder is removably mounted to a main body of the SCM to provide access to the piston end bearing and the linear actuator is removably mounted to the main body to provide access to the drive end bearing.
10 . The SCM as claimed in claim 1 , wherein the SCM comprises an anti-rotation mechanism to prevent or limit relative rotation between the piston and cylinder.
11 . The SCM as claimed in claim 10 , wherein the anti-rotation mechanism comprises at least one permanent magnet fixed to one of the moving part and stationary part to interact with a member formed from a magnet material fixed to the other one of the moving part and stationary part.
12 . The SCM as claimed in claim 10 , wherein the anti-rotation mechanism comprises a pair of permanent magnets fixed to one of the moving part and stationary part to interact with a pair of members formed from a magnet material fixed to the other one of the moving part and stationary part, and wherein the pair of permanent magnets are arranged with opposed polarities interacting with the corresponding pair of members.
13 . The SCM as claimed in claim 1 , wherein the SCM comprises a support mechanism to support the weight of the moving assembly.
14 . The SCM as claimed in claim 13 , wherein the support mechanism comprises at least one lifting permanent magnet arranged above or below the moving part of the linear actuator to attract or repel the moving part to support the weight of the moving assembly.
15 . The SCM as claimed in claim 13 , wherein the support mechanism is configured to provide a lifting force substantially equal to the weight of the moving assembly.
16 . The SCM as claimed in claim 13 , wherein the support mechanism supports the moving assembly approximately at the centre of its stroke with the SCM unpowered.
17 . The SCM as claimed in claim 13 , wherein a force generated by an electrical current in one or more coils of the linear actuator is sufficient to drive reciprocation of the moving assembly without substantially providing a force required to support the weight of the moving assembly.
18 . The SCM as claimed in claim 1 , wherein the SCM comprises a heatsink in thermal contact with wire coil(s) of the actuator, and wherein the heatsink forms a housing around at least part of the linear actuator.
19 . The SCM as claimed in claim 18 , wherein the heatsink extends above and below the stationary part of the linear actuator to shield personnel from a magnetic field of the linear actuator.
20 . The SCM as claimed in claim 1 , the SCM comprising: a position sensor configured to sense a position of the moving part of the actuator, and a controller configured to deliver an electrical current to the wire coil(s) based on a position signal from the position sensor to drive a sinusoidal reciprocating motion of the moving part of the actuator.

Description

CORRESPONDING APPLICATION This application is bypass continuation application of International Patent Application PCT/IB2025/053673 which is based on the provisional specification filed in relation to U.S. Patent Application No. 63/641,147, the entire contents all of which is incorporated herein by reference. TECHNICAL FIELD This invention relates to a streaming current monitor (SCM) for use in measuring the charge characteristic of a colloid, and in particular for use in determining a coagulant dosage rate in a water treatment plant. BACKGROUND A Streaming Current Monitor (SCM) is used to measure a charge characteristic of a colloid. The charge characteristic can be used to determine an amount of coagulant to be dosed to a colloid to cause the particles of the colloid to flocculate and be separated from the fluid medium of the colloid, e.g. by sedimentation, filtration or other separation method. An SCM has a piston received in a cylinder. A motor and gear box arrangement drives the piston via a linkage or eccentric cam to reciprocate in the cylinder. The reciprocating piston draws colloid into and out of the cylinder to pass over a pair of electrodes. The electrodes provide a streaming current sensor which can be calibrated to provide a direct real-time measure of the charge characteristic of the colloid which is related to the number of particles in suspension in the fluid medium of the colloid. Coagulant is added to the colloid to neutralise the charge of the suspended particles, causing the particulars to flocculate. SCM are used in water (e.g. fresh water and waste water) treatment plants to provide real time feedback control the amount of coagulant required to separate the solids from the water in real time. The SCM is used to continuously measure the charge characteristic after a rapid mixing stage where coagulant is mixed with the colloid. A dosing controller adjusts the coagulant dosing rate to maintain a set streaming current output from the SCM to optimise the amount of coagulant dosed to the system. Reliability issues have plagued prior art streaming current monitors. The motor and gear box arrangement of prior art SCMs generate excessive heat which must be dissipated. The effect of wear and tear on the moving parts including measurement surfaces and drive mechanisms results in significant measurement errors. Any unevenness in the piston stroke due to misalignment or looseness in the mechanical drive will translate directly into a distortion of the streaming current signal. Changes in the condition of the sensing surfaces will change the manner in which they become coated with colloidal material and equilibrium constants between the surfaces and the solution. These effects are normally the most significant on the surface of the piston. Once the wear reaches a certain level the streaming current reading produced becomes unstable, and commonly drifts in an unpredictable manner. The reference to any prior art in the specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in any country. DISCLOSURE OF INVENTION It is an object of the present invention to address any one or more of the above problems or to at least provide the industry with a useful choice. According to one aspect of the present invention there is provided a streaming current monitor (SCM), the SCM comprising: an inlet and an outlet to receive and deliver a flow of colloid to and from the SCM;a cylinder in fluid communication with a flow-path between the inlet and outlet, and a piston received in the cylinder to reciprocate therein,a drive mechanism to drive reciprocation of the piston in the cylinder to move colloid into and out of the cylinder via an annular space between the piston and cylinder,a pair of electrodes exposed in a wall of the cylinder and spaced apart in a moving direction of the piston, anda shaft extending between the piston and the drive mechanism, whereinthe drive mechanism is a linear actuator comprising a stationary part and a moving part, the moving part connected to the shaft. In some embodiments, the moving part of the linear actuator comprises a permanent magnet and the stationary part comprises at least one wire coil to generate a magnetic force to cause the moving part, shaft and piston to reciprocate. In some embodiments, the stationary part comprises two wire coils spaced apart in a moving direction of the moving part, a first coil primarily interacts with a north end of the permanent magnet and a second coil primarily interacts with a south end of the permanent magnet. In some embodiments, the SCM comprises at least one magnetic position sensor to provide an indication of a position of the permanent magnet of the moving part of the linear actuator, the at least one position sensor located at an axial centre region of the permanent magnet. In some embodiments, the at least one position sensor comprises