GB2122002A - Fluid flow monitoring - Google Patents

Abstract

Electronic circuitry (4, 7) is disclosed for use with a fluid flow monitor. The monitor (1) comprises sensing means (2) for use in sensing whether steam is passing through a steam trap (3) or is not passing through the steam trap, which electronic circuitry is coupled with the sensing means and has i) indication producing means (5, 6) for providing an indication of a first kind if the sensing means is in a first condition, indicative of steam passing through the steam trap, and an indication of a second kind if the sensing means is in a second condition, indicative of steam not passing through the steam trap, and ii) means whereby such an indication of the first kind is not produced unless the sensing means is in the said first condition for greater than a first predetermined time and such an indication of the second kind is not produced unless the sensing means is in the said second condition for greater than a second predetermined time. <IMAGE>

Description

SPECIFICATION Fluid flow monitoring The present invention relates to fluid flow monitoring.

According to the present invention, there is provided electronic circuitry for use with a fluid flow monitor, the monitor comprising sensing means for use in sensing whether steam is passing through a steam trap or is not passing through the steam trap, which electronic circuitry may be coupled with such sensing means and has i) indication producing means for providing an indication of a first kind if the sensing means as in a first condition, indicative of steam passing through the steam trap, and an indication of a second kind if the sensing means is in a second condition, indicative of steam not passing through the steam trap, and ii) means whereby such an indication of the first kind is not produced unless the sensing means is in the said first condition for greater than a first predetermined time and such an indication of the second kind is not produced unless the sensing means is in the said second condition for greater than a second predetermined time.

The present invention also comprises a combination of such a fluid flow monitor and electronic circuitry according to the preceding paragraph coupled with the sensing means of the monitor.

The combination could include a plurality of such monitors, the sensing means of which are each coupled with the said electronic circuitry and the latter being arranged for scanning, in a multiplexing manner, the sensing means.

The or each such fluid flow monitor could comprise a chamber having an inlet and an outlet whereby the chamber can be connected in a steam flow line to serve as a receptacle for condensate; a baffle between the inlet and the outlet in that part of the chamber inwhich condensate can collect: and an electrode extending into the interior of the said part of the chamber in which condensate can collect, the electrode comprising the sensing means of the monitor and the baffle being apertured above the level of the electrode and being disposed such that, in use, a steam flow induced pressure drop at the outlet of the chamber results in a fall in the level of the collected condensate at the inlet side of the baffle, and the electrode serving for ascertaining change in condensate level to a predetermined extent brought about by steam flow induced pressure drop at the outlet, the electrode being electrically insulated from an electrically conductive area exposed to the collected condensate and positioned such that, in use, change in condensate level to a predetermined extent brought about by pressure drop at the outlet breaks an electrically conductive path from the electrode via the condensate to the electrically conductive area, the electronic circuitry being coupled with the said electrode and its indication producing means providing the said indication of a first kind if the electrode is in a condition indicative that the said electrically conductive path exists, and the said indication of a second kind if the electrode is in a condition indicative that the said electrically conductive path is broken.

The said second time could be longer than the said first time.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a fluid flow monitoring system; Figure 2 shows a monitor of the system; Figure 3 is a block diagram for explaining the function of an indicator unit of the system; Figures 4 and 5 are circuit diagrams showing details of the indicator unit; and Figure 6 is a circuit diagram of a power supply unit for the indicator unit.

Our British Patent Application No. 42099/78 (Serial No. 2,022,846) describes forms of fluid flow monitors for use in steam flow lines. For monitoring purposes, an electrode of such a monitor is in circuit with a power source, such as a dry battery, and indicator lights in a control box, the circuit being such that one of the lights (which can be a green light) is illuminated if the circuit is completed because the electrode is submerged in condensate, resulting in an electrically conductive path from the electrode to an electrically conductive mounting therefor (which mounting is electrically insulated from the electrode) via the condensate, whereas another light (which can be red) is illuminated if the electrode is not submerged and the path just mentioned is therefore broken.Our above-mentioned British patent application also mentions that several such monitors may be connected in turn to a single control box.

The following example of the present invention is in a system in which several such monitors are used to monitor respectively several steam traps, to indicate when a failure occurs in any of the respective steam traps being monitored, electronic circuitry scanning the monitors continuously in a multiplexing manner.This is schematically illustrated in Figure 1, in which reference numeral 1 indicates one of twelve monitors according to our above-mentioned British patent application, reference numeral 2 indicating the electrode thereof; reference numeral 3 indicates one of twelve steam traps, each being monitored by a respective one of the monitors 1; reference numeral 4 indicates an indicator unit which is fed from the electrodes 2 of the monitors 1, reference numeral 5 indicating a green light emitting diode (LED) light and reference numerals 6 denoting twelve red LED lights; reference numeral 7 indicates a power supply unit for the indicator unit 4; and reference numeral 8 indicates a line from the power supply unit 7, for example to a building management system computer.In operation, if all the steam traps being monitored are working correctly, then the green LED light 5 is illuminated on the indicator unit as a "pass" light whereas if one or more of the traps is blowing steam, then the corresponding one or ones of the red LED lights 6 is or are illuminated as one or more "fail" lights and the light 5 is extinguished. This provides a visual indication on the unit 4, which is energised continuously, either that all steam traps are working correctly or that there is steam being lost from a particular one or particular ones of identified steam traps. The power supply unit 7 provides a low voltage supply for the indicator unit 4 and is designed such that it may provide the low voltage supply selectively either from a +24 volts d.c. supply or a 1 10/220/240 volts a.c. supply.

The line 8 enables failure of one or more steam traps to be automatically announced in a central control.

The indicator unit 4 is designed in such a way that it substantially overcomes the following problem associated with the fact that, in practice, the signal coming from the electrode 2 of a monitor is not always a straightforward "pass" of "fail" signal. This problem will be described with reference to Figure 2, which shows a fluid flow monitor 1 according to our above-mentioned British patent application, references 9 and 10 indicating the inlet and outlet respectively of the monitor, reference 11 indicating condensate in the monitor, reference 12 indicating the baffle of the monitor, reference 13 indicating the aperture in the baffle and reference 14 indicating the mounting for the electrode 2. Consider a steam trap that is stuck open. Steam will be leaking away but condensate, coming from the plant being drained, will also be passing through the trap.In the monitor 1 , the water level upstream of the baffle 1 2 will be depressed but condensate will be flowing into the monitor chamber and may sometimes splash the electrode 2 as depicted in Figure 2. In an arrangement as described in our above-mentioned British patent application, on the control box the red light would be illuminated most of the time but an occasional green flash would occur. However, an operator would ignore these short flashes and correctly note that the trap had failed. However, in an arrangement according to Figure 1, it would be disadvantageous if such spurious indications were produced on the line 8.

Consider now the case of a steam trap that discharges intermittently. When the trap is closed, the green light on the control box of an arrangement as described in our above-mentioned British patent application will be illuminated but the periodic discharge may be violent enough to purge the condensate from the monitor's chamber. If this happens, the red light will show for a short period. Similarly to the previous case, an operator is able to recognise such cyclic performance and allow for it when interpreting the control box's indication but it would disadvantageous is such spurious indications occurred on the line 8.

Thus, there can occur spurious "pass" signals when a steam trap has failed or, on another occasion, intermittent "fail" signals when a trap is working correctly. Moreover, during plant start up, the lights on the control box in an arrangement as described in our above-mentioned British patent application will flash alternately due to air being discharged from the pipe line and fluctuations in line pressure and, again, it would be disadvantageous if such spurious indications occurred on the line 8.

To substantially overcome the above problems, the indicator unit 4 is designed to be capable of differentiating between false and true signals. This is achieved by building inhibiting filters into the circuitry of the unit connected with the electrodes of the monitors, as schematically illustrated in Figure 3, in which block A indicates a resistance detector for detecting the resistance between the electrode 2 and the mounting 14 of a monitor; reference B indicates a filter which ensures that the green "pass" condition is not accepted until such a signal has been present for half a second for example, i.e. the system ignores the short "pass" pulses caused by splashing of the electrode; reference C indicates a filter for preventing a "fail" condition being indicated until that condition has been maintained for ten minutes for example, this filter catering for the case where condensate has been swept out of the monitor chamber by a blast action steam trap; and reference D indicates the display of LEDs.

Each of the twelve input lines to the indicator unit 4 from the electrodes 2 of the monitors is filtered separately and, to conserve components, multiplexing techniques are used whereby the arrangement according to Figure 3 is used for each of the lines in a time-shared multiplexing manner. Either the "pass" green LED is illuminated on the indicator unit or one or more red "fail" LEDs are illuminated to indicate which particular steam trap or steam traps is or are blowing steam.

The line 8 from the power supply 7, which line can be connected to a building management system computer, is triggered by a change in the current being drawn in the indicator unit 4. If all steam traps are operating correctly, the indicator 4 draws a little current whereas if one or more fail conditions exist, it is arranged that the current flow increases significantly.

The indicator unit 4 includes, for realising the above, a printed circuit board for multiplexing and filtering purposes (whose circuitry is shown in Figure 4) and a printed circuit board for display purposes (whose circuitry is shown in Figure 5).

Referring to these figures, the indicator unit allows for the monitoring of twelve steam traps, each by a respective monitor 1, the electrodes 2 of the monitors being connected to respective ones of input terminals 21, 22,23... 29,210,211 and 212 of the multiplexing and filtering circuit board. Each of the twelve monitors is interrogated approximately every minute and the result "pass" (a detected resistance of less than 200 KQ for example) or "fail" (a detected resistance of greater than 220is1 for example) is latched before being applied to the display printed circuit board.The scanning is achieved by the use of analogue multiplexers provided by integrated circuits IC1 and IC2 controlled via inputs from integrated circuits IC4, IC5 and IC6. The outputs from the multiplexers are commanded in turn and each monitor forms the fourth leg of a bridge circuit. When the respective trap is in a "fail" state, the output at pin 1 of integrated circuit IC3 will be in a low state aimost continuously, whereas for a "pass" state, this output will oscillate at the drive frequency to the bridge. For the above conditions, the output at pin 2 of integrated circuit IC3 will be low for a "pass" state and high for a "fail" state.Latching of the states is provided by eight-bit addressable latches provided by integrated circuits IC8 and IC9 whose terminals 1 A, 2A, 3A, 1 A and 1 2A are connected to respective input terminals 1 B, 2B,3B... 1 B and 1 2B of the display printed circuit board. The integrated circuits IC8 and IC9 are again addressed by integrated circuits IC4, IC5 and IC6 the strobes required to latch the states being provided by the outputs at pins 1 and 13 respectively of an integrated circuit IC7.

Timing for the circuitry of Figure 4 is provided by an oscillator whose output is at pin 1 5 of integrated circuit IC4, the oscillator frequency being set at a nominal 1.75kHz. This, via a divider provided by integrated circuits IC5 and IC6, provides a ten minute clock for the display circuit board. The output at pin 9 of integrated circuit IC5, buffered by the integrated circuit IC4, provides the required a.c. energisation via a capacitor C5 to the bridge.

When the output at pin 11 (Q2) of the integrated circuit IC6 is low, the multiplexer IC1 is selected and the address from pin 2 of integrated circuit IC5, pin 3 of integrated circuit IC5 and pin 12 of integrated circuit IC6 selects the relevant monitor to be sensed. With the output at pin ii of integrated circuit IC6 low, the output at pin 1 of integrated circuit IC7 is enabled via the output at pin 4 of integrated circuit IC4, and the outputs at pins 14, 1 5 and 1 of integrated circuit IC5, gated by the integrated circuit IC7, provide a strobe pulse to pin 4 of integrated circuit IC8, which is addressed by the same address as the multiplexer.

With the output at pin 11 of integrated circuit IC6 high, the multiplexer IC2 is selected and the strobe pulse from pin 13 of the integrated circuit IC7 loads integrated circuit IC9 via its pin 4.

To allow for testing, a link is introduced at LK2 so that the output at pin 4 of integrated circuit IC6 may be made to toggle at a rate faster than ten minutes. This is achieved by injecting a suitable clock at the junction of link terminals LK1 and pin 1 of integrated circuit IC6. Alternatively, the output of the oscillator may be used for this purpose.

The values of resistors R1, R2, R5 are chosen to be equal to the "fail" resistance for a monitor, while resistor R8 and capacitor C2 form a low pass filter with a 5Hz cut-off frequency. The network comprising resistors R9 and R10 capacitor C3 and resistor R12 sets the trip level for the comparison between the "pass" and "fail" conditions and provides hysteresis plus noise immunity for the decision. Resistors R7 and R 11 are "pull-ups" for the open collector outputs of the comparator. Delaying the output at pin 14 of integrated circuit IC5 by resistor R6 and capacitor C4 substantially removes any interference from the outputs of integrated circuit IC7 due to the asynchronous nature of the counters.Resistors R13 and R1 4 and capacitor C1 set the oscillator frequency fto: f - 0.559/RC, where R1 = R2 = R In Figure 5, diodes D1, D2 ... D11 and D12 are the red LEDs 6 and diode D15 is the green LED 5.

Figure 6 is a circuit diagram of the power supply unit 7. This unit is designed to work from external supplies of 24 volts d.c. and 110/220/240 a.c. Standard circuit techniques are employed for the d.c. input derived from the mains. The d.c. input supply to a regulator provided by an integrated circuit It 17 is 18 volts nominal and there is provided a +7.5 volts supply for the circuitry of Figures 4 and 5, there also being the need to provide a -7.5 volts supply and the current sensing technique. This is achieved by using the +7.5 volts supply from the regulator IC17 via a positive to negative voltage converter provided by an integrated circuit IC18 to supply the -7.5 volts.The nominal +7.5 volts to the circuitry of Figures 4 and 5 is allowed to vary between +7.5 volts and +6.9 volts for current sensing purpose, with this variable voltage being sensed by a comparator provided an integrated circuit IC19 whose output drives the coil of a relay R, which coil is connected to the input of regulator IC17. The current sense level is set at 33mA. This lies approximately half way between the "pass" current (15mA) and the "fail" current (45mA) of the multiplexer circuitry, allowing maximum noise immunity for the comparator. Initial adjustment of the +7.5 volts supply is provided by potentiometer R26 and this adjustment should be made with the power supply unit off load.

For a mains input, the voltage selected is achieved using links at particular ones of link terminals LK3 to LK7, the following list detaiiing the link settings for 11 0, 220, 240 volts: VOLTAGE LINKS FITTED AT 110 LK4,LK3,LK7 220 LK5, LK6 240 LK7, LK5

Claims (7)

1. Electronic circuitry for use with a fluid flow monitor, the monitor comprising sensing means for use in sensing whether steam is passing through a steam trap or is not passing through the steam trap, which electronic circuitry may be coupled with such sensing means and has i) indication producing means for providing an indication of a first kind if the sensing means is in a first condition, indicative of steam passing through the steam trap, and an indication of a second kind if the sensing means is in a second condition, indicative of steam not passing through the steam trap, and ii) means whereby such an indication of the first kind is not produced unless the sensing means is in the said first condition for greater than a first predetermined time and such an indication of the second kind is not produced unless the sensing means is in the said second condition for greater than a second predetermined time.

2. A combination of electronic circuitry according to claim 1, and such a fluid flow monitor, the circuitry being coupled with the sensing means of the monitor.

3. A combination according to claim 2, which includes a plurality of such monitors, the sensing means of which are each coupled with the said electronic circuitry and the latter being arranged for scanning, in a multiplexing manner, the sensing means.

4. A combination according to claim 2 or 3, wherein the or each fluid flow monitor comprises a chamber having an inlet and an outlet whereby the chamber can be connected in a steam flow line to serve as a receptacle for condensate; a baffle between the inlet and the outlet in that part of the chamber in which condensate can collect; and an electrode extending into the interior of the said part of the chamber in which condensate can collect, the electrode comprising the sensing means of the monitor and the baffle being apertured above the level of the electrode and being disposed such that, in use, a steam flow induced pressure drop at the outlet of the chamber results in a fall in the level of the collected condensate at the inlet side of the baffle, and the electrode serving for ascertaining change in condensate level to a predetermined extent brought about by steam flow induced pressure drop at the outlet, the electrode being electrically insulated from an electrically conductive area exposed to the collected condensate and positioned such that, in use, change in condensate level to a predetermined extent brought about by pressure drop at the outlet breaks an electrically conductive path from the electrode via the condensate to the electrically conductive area, the electronic circuitry being coupled with the said electrode and its indication producing means providing the said indication of a first kind if the electrdë is in a condition indicative that the said electrically conductive path exists, and the said indication of a second kind if the electrode is in a condition indicative that the said electrically conductive path is broken.

5. Electronic circuitry according to claim 1 or a combination according to any of claims 2 to 4, wherein the said second time is longer than the said first time.

6. Electronic circuitry for use with a fluid flow monitor, substantially as herein described with reference to and as illustrated in Figures 3, 4, 5 and 6 of the accompanying drawings.

7. A combination of a fluid flow monitor and electronic circuitry coupled therewith, substantially as herein described with reference to and as illustrated in the accompanying drawings.