GB2108673A

GB2108673A - Indicating direction of fluid flow

Info

Publication number: GB2108673A
Application number: GB08131690A
Authority: GB
Inventors: Kevin David Reed
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1981-10-21
Filing date: 1981-10-21
Publication date: 1983-05-18

Abstract

A device comprises a sensor in the form of a pair of thermistors 9 and 10, for insertion in a fluid flow. The thermistors 9 and 10 form one branch of a Wheatstone bridge 20 and the output from their junction forms an input to the negative terminal of an operational amplifier IC-1. In use, one thermistor disposed upstream from the other thermistor will be cooled relative to the other thermistor causing an out of balance signal to appear at the junction between the thermistors 9 and 10. Depending on which thermistor is cooled the signal so appearing will be high or low. Means, in the form of two light emitting diodes LED-1 and LED-2 arranged in parallel and with opposite polarity, indicate whether the signal is high or low. If the signal is low LED-1 will conduct whereas if the signal is high LED-2 will conduct. An external pointer on a probe carrying thermistors indicates the position of the thermistors and thus the direction of gas flow can be determined from the illuminated LED. <IMAGE>

Description

SPECIFICATION Gas flow direction indicator The present invention relates to a device for determining in which of two opposite directions a fluid, such as natural gas, is flowing in a duct, such as a gas main.

According to the present invention, there is provided a device for determining in which of two opposite directions a fluid is flowing in a duct, the device comprising a sensor for insertion in the duct and arranged to provide an electrical signal which is high when the fluid flows in one direction and which is low when the fluid flows in the opposite direction and means responsive to the signal for indicating whether the signal is high or low.

Preferably the sensor comprises a pair of serially connected thermistors arranged, in use, to be current conducting so as to be heated thereby.

In this case the thermistors are suitably arranged so that, in use, one thermistor is upstream of the other thermistor and is cooled by the flowing fluid while the other thermistor is shielded from the fluid by the upstream thermistor so that a differential voltage signal is produced at the junction of the thermistors.

Conveniently the thermistors form one arm of a wheatstone bridge.

Preferably the means for indicating whether the signal is high or low comprises a pair of parallel connected light emitting diodes arranged so that one diode conducts when the signal is high and the other diode conducts when the signal is low.

The thermistors are suitably incorporated in a probe adapted for insertion into the duct and conveniently form the probe tip.

Preferably the probe is provided with a pointer which, in use, is located externally of the duct and which indicates when one thermistor is shielded by the other.

An embodiment of the invention will now be particularly described by way of example only with reference to the accompanying drawings in which: Figure 1 is a side view of a probe located in use in a gas main carrying natural gas, Figure 2 is an enlarged view of the probe tip shown in Figure 1 and Figure 3 a diagram of a suitable circuit for use with the probe.

Referring to Figures 1 and 2, the probe 1 comprises a steel tube 2 extending through which are three connecting wires 3, 4, and 5. Wire 5 is located between wires 3 and 4 and splits into two arms 5a and 5b at its lower end. The wires 3, 4, and 5 are sealed in the tube end 6 by means of a silicone sealant 7. The end 6 of tube 2 is provided with a slight bulge 8 so as to prevent its inadvertent removal from a pipe gland.

Referring to Figure 2 the wires 3 and 5a are connected to a thermistor 9 while the wires 4 and 5b are connected to a thermistor 10. The thermistors 9 and 10 are conventional and are of the type whose resistance increases as their temperature falls. The thermistors 9 and 10 form a tip 11 to the probe 1 and are separated from each other by a silicone sealent 12.

Referring to Figure 1, a pointer 13 is secured to the top end 14 of the probe 1 so that the pointer 1 3 is externai of the gas main 1 5 when the probe tip 11 is located therein. The probe 1 can be axially rotated so that when the pointer 13 is arranged to point in a direction parallel to the longitudinal axis of the main 15, one thermistor is upstream of a downstream thermistor and shields the downstream thermistor from the flowing gas so that the upstream thermistor is cooled by the flowing gas more than the downstream thermistor.

In use, the probe 1 is inserted through a suitable gland 1 6 held in a plug 1 7. The plug 1 7 is screw fitted into an offtake pipe 18 extending outwardly from the wall of the main 15.

Referring to Figure 3, the circuit includes the pair of thermistors 9 and 10 connected in series and forming one arm of a wheatstone bridge 20.

The other arm is formed by two fixed resistors R1 and R2 and a potentiometer VR1 connected in series between the resistors R1 and R2. To overcome the possibility of thermal runaway destroying the thermistors 9 and 10 the bridge 20 is supplied by a constant current supply formed by resistors R3, and R4 and transistors TR1 and TR2.

The junction between the thermistors 9 and 10 is connected via a resistor R5 to the negative terminal of an opera.tional amplifier IC-l,the gain of the amplifier being controlled by a negative feedback resistor R6. The gain of the amplifier is set by the ratio of the two resistors R5 and R6.

The positive terminal of the amplifier IC-l is connected to the potentiometer VR 1.

The output from the amplifier is supplied via a resistor R7 to a pair of parallel connected light emitting diodes LED-1 and LED-2 arranged in opposite polarity, the resistor R7 serving to limit the current to the diodes. Power is supplied to the circuit via two batteries B-l and B-2 switched by switches SW-1 and SW-2.

When the switches SW-1 and SW-2 are activated both thermistors 9 and 10 are heated by current flow therethrough and the potentiometer VR-1 is adjusted until the bridge 20 is balanced.

When the probe 1 is inserted in the main 14 and rotated until one thermistor is upstream of the other thermistor and shields the other thermistor from the flowing gas, the upstream thermistor will be cooled more than the downstream thermistor and its resistance will change. This will cause the bridge 20 to be unbalanced and the signal so produced will be amplified by the amplifier IC-l.

If thermistor 9 is being cooled (ie. is upstream) its resistance will be higher than thermistor 10 and consequently a low or negative signal will be output at the junction of the thermistors 9 and 10 and this will appear at the output of the amplifier IC-l as a high signal. This will cause diode LED-1 to conduct.

If on the other hand thermistor 10 is being cooled (ie. is upstream) its resistance will be higher than thermistor 9 and consequently a high or positive signal will be output at the junction of the thermistors 9 and 10 and this will appear at the output of the amplifier IC-l as a low signal.

This will cause diode LED-2 to conduct.

Thus, if diode LED-2 conducts, thermistor 10 must be the upstream thermistor and if diode LED-1 conducts, thermistor 9 must be the upstream thermistor. It is thus possible to determine in which direction the gas is flowing.

The diodes may be of different colours, for instance, LED-1 may be green and LED-2 may be red. LED-1 may be illuminated if the pointer is arranged to indicate the direction of flow and LED-2 may be illuminated if the flow is in the opposite direction.

Claims

1. A device for determining in which of two opposite directions a fluid is flowing in a duct, the device comprising a sensor for insertion in the duct and arranged to provide an electrical signal which is high when the fluid flows in one direction and which is low when the fluid flows in the opposite direction and means responsive to the signal for indicating whether the signal is high or low.

2. A device as claimed in Claim 1 in which the sensor is a pair of serially connected thermistors arranged, in use, to be current conducting so as to be heated thereby.

3. A device as claimed in Claim 2 in which the thermistors are arranged so that, in use, one thermistor is upstream of the other thermistor and is cooled by the flowing fluid while the other thermistor is shielded from the fluid by the upstream thermistor so that a differential voltage signal is produced at the junction of the thermistors.

4. A device as claimed in Claim 2 or Claim 3 in which the thermistors form one arm of a wheatstone bridge.

5. A device as claimed in any of Claims 1 to 4 in which the means for indicating whether the signal is high or low comprises a pair of parallel connected light emitting diodes arranged so that one diode conducts when the signal is high and the other diode conducts when the signal is low.

6. A device as claimed in any of Claims 2 to 5 in which the thermistors are incorporated in a probe adapted for insertion into the duct.

7. A device as claimed in Claim 6 in which the thermistors form the probe tip.

8. A device as claimed in Claim 7 or Claim 8 in which the probe is provided with a pointer which, in use, is located externally of the duct and which indicates when one thermistor is shielded by the other.

9. A device substantially as hereinbefore described with reference to the accompanying drawings.