GB1581327A - Detection of levels in conductive oils - Google Patents

Detection of levels in conductive oils Download PDF

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Publication number
GB1581327A
GB1581327A GB5138275A GB5138275A GB1581327A GB 1581327 A GB1581327 A GB 1581327A GB 5138275 A GB5138275 A GB 5138275A GB 5138275 A GB5138275 A GB 5138275A GB 1581327 A GB1581327 A GB 1581327A
Authority
GB
United Kingdom
Prior art keywords
reservoir
probe
level
detector
warning device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB5138275A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thomas Electronics Ltd
Original Assignee
Thomas Electronics Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomas Electronics Ltd filed Critical Thomas Electronics Ltd
Priority to GB5138275A priority Critical patent/GB1581327A/en
Publication of GB1581327A publication Critical patent/GB1581327A/en
Expired legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G01F23/241Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid for discrete levels

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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Valves And Accessory Devices For Braking Systems (AREA)
  • Emergency Alarm Devices (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Description

(54) IMPROVEMENTS IN OR RELATING TO THE DETECTION OF LEVELS IN CONDUCTIVE OILS (71) We, THOMAS ELECTRONICS LIMITED, a British Company of 69 Strines Road, Marple, Cheshire, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the detection of levels in conductive oils, such as vegetable oils used for example in vehicle hydraulic brake and clutch systems.
There is a need for a level detecting device which will give warning when the level of hydraulic oil in a brake or clutch system falls below a safe level.
An object of the invention is to provide a detector device which is capable of giving a warning when the level of a conductive oil in a system falls below a predetermined level.
According to the invention, there is provided a detector for detecting a level of a conductive oil in a reservoir, comprising a probe for mounting in the reservoir at the level to be detected, and a circuit means for connection to the probe for sensing the current flow from the probe through the oil to the reservoir or a ground electrode for operating a warning device when the level to be detected is reached, characterised in that a test circuit is provided for indicating that the detector is operative when the circuit means is first connected to an energising source, the test circuit comprising a capacitor arranged to be charged at a predetermined rate when the circuit means is first energised and to cause the operation of the warning device until charged.
An embodiment of the invention will now be described with reference by way of example to the accompanying drawing which is a schematic circuit diagram of a level detector in accordance with the invention.
A reservoir 1 has secured therein by an insulating bush 2, a probe 3 which is connected to a terminal 4. The reservoir 1 is connected to earth by its mountings or, for example, to ground terminal 5 so that a small current, say 1 microamp, flows from the supply rail 6 through resistors R5 and R6, the probe 3 and brake fluid 7 to the earthed reservoir 1. The normal level of fluid 7 is shown at 8.
Transistors T1 and T2 together with associated resistors R1, R2, R3 and R4 form a differential amplifier, the base of transistor T2 being connected to the junction of resistors R5 and R6. The small current through probe 3 is sufficient to maintain transistor T2 in conduction. The collector of transistor T2 is connected to the base of a transistor T3 which is reverse biased when transistor T2 is in conduction. Transistor T3 together with transistors T4 and T5 and associated circuits form an amplifier to operate a warning device 9 which may be visual and/or audible. Transistor T3 maintains reverse bias on transistors T4 and T5, when it is itself reverse biased.
Should the level of liquid 7 fall below the position of probe 3, i.e. to the minimum level indicated by broken line 10, the current through the probe will markedly reduce to the leakage current causing transistor T2 to become reverse biased and its collector to become rapidly negative in accordance with the normal action of a differential amplifier. This now allows transistor T3 to become forward biased causing transistor T4 and T5 to conduct enabling warning device 9 to operate. When the level of the liquid is restored warning device 9 again become inoperative.
A diode D1 inserted in the supply rail 6 protects the circuit against damage if the supply source to be connected across terminals 11 and 12 is wrongly polarised.
Capacitor Cl and resistor R12 provide a test circuit when the supply voltage is first applied, i.e. the equipment is first switchedon after a period of non-use. Capacitor Cl charges through resistor R12 and the baseemitter path of transistor T4, causing transistors T4 and T5 to become conductive and alarm device 9 to operate. As soon as capacitor Cl becomes charged, the charging time being dependent on the time constant involved, transistor T4 becomes and is maintained reverse biased as described above. However, there has been a temporary operation of the warning device which checks its satisfactory operation.
In one example of the invention, used in conjunction with the brake fluid reservoir of a motor vehicle, satisfactory operation was obtained between temperatures between 40tC and +90"C and with probe-toreservoir resistance between 0 and 5 megohms.
WHAT WE CLAIM IS: 1. A detector for detecting a level of a conductive oil in a reservoir, comprising a probe for mounting in the reservoir at the level to be detected, and a circuit means for connection to the probe for sensing the current flow from the probe through the oil to the reservoir or a ground electrode for operating a warning device when the level to be detected is reached, characterised in that a test circuit is provided for indicating that the detector is operative when the circuit means is first connected to an energising source, the test circuit comprising a capacitor arranged to be charged at a predetermined rate when the circuit means is first energised and to cause the operation of the warning device until charged.
2. A detector according to claim 1, wherein the probe is mounted in an insulating bush located in a conductive reservoir, the reservoir being connected to earth by the mountings or to a ground terminal.
3. A detector according to claim 1 or 2, wherein the circuit means comprises a differential amplifier.
4. A detector according to any preceding claims, wherein the warning device comprises a visual and/or audible device.
5. A detector for detecting a level of a conductive oil in a reservoir substantially as hereinbefore described with reference to the accompanying drawings.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. applied, i.e. the equipment is first switchedon after a period of non-use. Capacitor Cl charges through resistor R12 and the baseemitter path of transistor T4, causing transistors T4 and T5 to become conductive and alarm device 9 to operate. As soon as capacitor Cl becomes charged, the charging time being dependent on the time constant involved, transistor T4 becomes and is maintained reverse biased as described above. However, there has been a temporary operation of the warning device which checks its satisfactory operation. In one example of the invention, used in conjunction with the brake fluid reservoir of a motor vehicle, satisfactory operation was obtained between temperatures between 40tC and +90"C and with probe-toreservoir resistance between 0 and 5 megohms. WHAT WE CLAIM IS:
1. A detector for detecting a level of a conductive oil in a reservoir, comprising a probe for mounting in the reservoir at the level to be detected, and a circuit means for connection to the probe for sensing the current flow from the probe through the oil to the reservoir or a ground electrode for operating a warning device when the level to be detected is reached, characterised in that a test circuit is provided for indicating that the detector is operative when the circuit means is first connected to an energising source, the test circuit comprising a capacitor arranged to be charged at a predetermined rate when the circuit means is first energised and to cause the operation of the warning device until charged.
2. A detector according to claim 1, wherein the probe is mounted in an insulating bush located in a conductive reservoir, the reservoir being connected to earth by the mountings or to a ground terminal.
3. A detector according to claim 1 or 2, wherein the circuit means comprises a differential amplifier.
4. A detector according to any preceding claims, wherein the warning device comprises a visual and/or audible device.
5. A detector for detecting a level of a conductive oil in a reservoir substantially as hereinbefore described with reference to the accompanying drawings.
GB5138275A 1975-12-16 1975-12-16 Detection of levels in conductive oils Expired GB1581327A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB5138275A GB1581327A (en) 1975-12-16 1975-12-16 Detection of levels in conductive oils

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB5138275A GB1581327A (en) 1975-12-16 1975-12-16 Detection of levels in conductive oils

Publications (1)

Publication Number Publication Date
GB1581327A true GB1581327A (en) 1980-12-10

Family

ID=10459784

Family Applications (1)

Application Number Title Priority Date Filing Date
GB5138275A Expired GB1581327A (en) 1975-12-16 1975-12-16 Detection of levels in conductive oils

Country Status (1)

Country Link
GB (1) GB1581327A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2166870A (en) * 1984-07-30 1986-05-14 Dominic N Loiacono Liquid level detection
US4849739A (en) * 1984-07-30 1989-07-18 Ala Inc., A New Jersey Corporation Liquid detector for air pressure type fire sprinkler system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2166870A (en) * 1984-07-30 1986-05-14 Dominic N Loiacono Liquid level detection
US4849739A (en) * 1984-07-30 1989-07-18 Ala Inc., A New Jersey Corporation Liquid detector for air pressure type fire sprinkler system
GB2166870B (en) * 1984-07-30 1989-07-19 Dominic N Loiacono Liquid detector for air pressure type fire sprinkler system

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PCNP Patent ceased through non-payment of renewal fee