GB2066485A - Alarm or detection circuit - Google Patents
Alarm or detection circuit Download PDFInfo
- Publication number
- GB2066485A GB2066485A GB8038950A GB8038950A GB2066485A GB 2066485 A GB2066485 A GB 2066485A GB 8038950 A GB8038950 A GB 8038950A GB 8038950 A GB8038950 A GB 8038950A GB 2066485 A GB2066485 A GB 2066485A
- Authority
- GB
- United Kingdom
- Prior art keywords
- bridge
- arm
- arms
- resistor
- diode
- 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.)
- Granted
Links
- 238000001514 detection method Methods 0.000 title description 2
- 230000001419 dependent effect Effects 0.000 claims description 2
- 239000007788 liquid Substances 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B25/00—Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems
- G08B25/008—Alarm setting and unsetting, i.e. arming or disarming of the security system
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating 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
- G01F23/24—Indicating 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
- G01F23/241—Indicating 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
- G01F23/243—Schematic arrangements of probes combined with measuring circuits
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R17/00—Measuring arrangements involving comparison with a reference value, e.g. bridge
- G01R17/10—AC or DC measuring bridges
- G01R17/16—AC or DC measuring bridges with discharge tubes or semiconductor devices in one or more arms of the bridge, e.g. voltmeter using a difference amplifier
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/02—Monitoring continuously signalling or alarm systems
- G08B29/04—Monitoring of the detection circuits
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Business, Economics & Management (AREA)
- Emergency Management (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- Emergency Alarm Devices (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
An indicator or detector device based on Wheatstone bridge principles has an operational amplifier (A) connected in the indication diagonal (3-4) and a square wave generator (Q) connected as the bridges voltage source in the other diagonals (1, 2). Two arms (1-3, 1-4) have resistors (R1, R2) in them, one of which (R2) is adjustable. The measuring arm (3-2) has a resistor (R5) which is responsive to the monitored condition in series with two diodes (D1, D2) in inverse parallel. The fourth arm (4-2) has two paralleled branches each of a resistor (R3, R4) in series with a diode (D3, D4), the diodes being in parallel inverse. This circuit can respond to either excessive reduction or excessive increases in the value of the monitored condition, as reflected by the value of the sensing resistor (R5). <IMAGE>
Description
SPECIFICATION
Alarm or detection circuit
The present invention relates to a circuit arrangement for a warning indicator or detector using a version of the Wheatstone bridge principle.
DE-OS 21 48 747 discloses a circuit arrangement for an electronic threshold switch of a warning indicator with a bridge circuit consisting of four impedances, in which a thyristor operating into a load is controlled by one of the bridge diagonals via a subcircuit consisting of two transistors and one resistor. Such a switch can respond in both directions of the variablility of one of the bridge resistors, i.e. a safe response is ensured both in case of a short circuit and in case of an interruption of a lead.
An object of the invention is to provide a circuit arrangement whose "hysteresis" can be varied.
According to the invention there is provided circuit arrangement for a warning indicator or detector, including a bridge circuit whose supply diagonal is connected to a voltage source and whose indication diagonal controls an operational amplifier, at least one arm of the bridge being dependent on a quantity to be monitored, two adjacent arms being resistors, and the other two
arms containing resistors, wherein
(a) the voltage source is a square-wave generator one terminal of which is connected to the junction point of the adjacent first and second bridge arms which are resistors;
(b) the other terminal of the square-wave generator is connected to the junction point of the adjacent third and fourth bridge arms;;
(c) in the third bridge arm, which is connected to the non-inverting input of the operational amplifier, a first diode and a second diode in inverse parallel are connected in series with the resistor;
(d) the fourth bridge arm, which is connected to the inverting input of the operational amplifier, contains a third diode and a fourth diode connected in inverse parallel via one adjustable resistor each, and
(e) the value of the resistor of the third bridge arm lies between the values of the resistors of the fourth bridge arm.
An embodiment of the invention will now be explained with reference to the accompanying drawing.
The bridge circuit has four arms Z1, Z2, Z3, Z4, and a square-wave generator Q serving as a voltage source has one terminal connected to the junction point 1 of the first arm Zl,which is a resistor Tri, and the second arm Z2, which is a resistor R2, the two arms being adjacent to each other. The resistor R2 is adjustable. The second terminal of the generator Q is connected to the junction point 2 of the two other bridge arms Z3 and Z4, i.e., of the third and fourth arms. The junction points 1, 2 are thus also the feeding points of the bridge.
In the third arm Z3, two diodes D1, D2 in inverse parallel are connected in series with the resistor R5, which is the measuring resistor which senses changes in resistance depending on the application. Thus it can respond to external changes, e.g. to changes in liquid levels, or to an interruption of a circuit, or to a short circuit. In a
burglar alarm, for example, the resistor R5 may
replace quite a number of resistors; in a liquidlevel gauge, it replaces the sensing element.
The first and third bridge arms Zi, Z3 are connected to the junction point 3 and to the noninverting input of an operational amplifier A, whose output is grounded through a visual or audible signal device 5. Where such a circuit is used in a control system, the output of the amplifier A may be connected to another element in that control system, in addition to or instead of to the visual or audible warning device. The inverting input of the operational amplifier A is connected to the junction point 4 of the second and fourth bridge arms Z2, Z4. The junction points 3 and 4 are the corners of the indication diagonal.
The fourth arm Z4 contains two diodes D3, D4 in inverse parallel, with the cathode of the diode D3 and the anode of the diode D4 connected to the junction point 2. Connected to the junction point 4 are a resistor R3 in series with the diode D3, and a resistor R4 in series with the diode D4, both resistors being adjustable.
The resistors R1 and R2 are adjusted to achieve equality, and the values of the resistors R3 and R4 are, respectively, above or below the value of the resistor R5, i.e., the value of the resistor R5 lies between those of the resistors R3, R4.
The circuit works as follows:
Assuming that the square-wave generator Q supplies voltage which is positive at the junction point 1 and at zero potential at the junction point 2, a current passes through the resistor R3 and the diode D3, and the voltage with respect to ground at the junction point 4 s positive with respect to that at the junction point 3. The output voltage of the operational amplifier A is then near zero potential.
By contrast, when the junction point 2 is at positive potential, and the junction point 1 is at zero potential, the current flows through the resistor R4 and the diode D4. Since the value of the resistor R4 is smaller than that of R5, the voltage at the junction point 4 is more positive than that at the junction point 3; thus, the output voltage of the operational amplifier A is again near zero. In both cases, the signal device 5 remains off.
When the value of R5 leaves the range limited by the values R3, R4, the voltage at the junction point 3 becomes more positive than that at the junction point 4, and the output voltage of the operational amplifier A lies near the supply voltage of the amplifier, so that the signal device 5 is turned on.
The hysteresis of the arrangement can thus be varied by means of the resistors R3, R4. The smaller the difference between the resistance values, the more sensitive the circuit arrangement will be.
The diodes D1, D2 serve to compensate for changes due to temperature and voltage variations in the values of the diodes D3, D4.
Such a circuit arrangement can be used wherever the quantity to be monitored influences the value of the resistor 5. It is especially suitable for use in a warning indicator which monitors the level of a liquid in a vessel or serves as a safeguard against burglary. Since the circuit arrangement also responds if the circuit is interrupted or shortcircuited, the wiring from a burglar alarm can be located outside the building, whereby costs are saved. The circuit arrangement has an additional advantage over the prior art in that its hysteresis can be varied by means of the resistors R3, R4, thus permitting its sensitivity to be adjusted.
Claims (3)
1. Circuit arrangement for a warning indicator or detector, including a bridge circuit whose supply diagonal is connected to a voltage source and whose indication diagonal controls an operational amplifier, at least one arm of the bridge being dependent on a quantity to be monitored, two adjacent arms being resistors, and -the other two arms containing resistors, wherein
(a) the voltage source is a square-wave generator one terminal of which is connected to the junction point of the adjacent first and second bridge arms which are resistors;
(b) the other terminal of the square-wave generator is connected to the junction point of the adjacent third and fourth bridge arms;
(c) in the third bridge arm, which is connected to the non-inverting input of the operational amplifier, a first diode and a second diode in inverse parallel are connected in series with the resistor;;
(d) the fourth bridge arm, which is connected to the inverting input of the operational amplifier, contains a third diode and a fourth diode connected in inverse parallel via one adjustable resistor each, and
(e) the value of the resistor of the third bridge arm lies between the values of the resistors of the fourth bridge arm.
New claims or amendments to claims filed on 31st March, 1981 Supersede,d claims
New or amended claims.
2. A circuit arrangement for an indicator or detector, based on a monitored condition, which arrangement includes a bridge circuit whose supply diagonal is connected to a voltage source formed by a square-wave generator; the indication diagonal of the bridge controlling an operational amplifier, wherein::
(a) at least one arm of the bridge includes a resistive impedance whose value depends on the monitored condition, two adjacent arms each of which is resistive, the other two arms, including resistive impedances;
(b) one terminal of the square-wave generator is connected to the junction of said firstmentioned two adjacent arms, the other terminal of the generator being connected to the junction of the said other two arms; ;
(c) the first-mentioned bridge arm, which includes the resistive impedance whose value depends on the monitored condition, is connected to the non-inverting input of the operational amplifier, and that arm includes first and second diodes connected in inverse parallel relation in series with the resistive impedance, and
(d) the fourth bridge arm, which is connected to the inverting input of a fourth diode connected in inverse parallel, each of said third and fourth diodes being in series with an adjustable resistive impedance, the adjustable impedances being so proportioned that one has a larger value than the resistive impedance in the first-mentioned bridge arm while the other has a smaller value than the resistive impedance in the first-mentioned arm.
3. A circuit arrangement for an indicator or detector substantially as described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19792952053 DE2952053A1 (en) | 1979-12-22 | 1979-12-22 | CIRCUIT ARRANGEMENT FOR A WARNING INDICATOR |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2066485A true GB2066485A (en) | 1981-07-08 |
| GB2066485B GB2066485B (en) | 1983-06-22 |
Family
ID=6089458
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8038950A Expired GB2066485B (en) | 1979-12-22 | 1980-12-04 | Alarm or detection circuit |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE2952053A1 (en) |
| GB (1) | GB2066485B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2584218A1 (en) * | 1985-06-26 | 1987-01-02 | Fichet Bauche | Surveillance installation for areas to be protected |
| FR2731070A1 (en) * | 1995-02-28 | 1996-08-30 | Commissariat Energie Atomique | Position measurement by potentiometric sensors |
| RU2153678C2 (en) * | 1998-10-12 | 2000-07-27 | Открытое акционерное общество "Ракетно-космическая корпорация "Энергия" им. С.П. Королева" | Device for visual monitoring of voltage value |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3714903A1 (en) * | 1987-05-05 | 1988-11-24 | Skt Podem | Overload limiter for lifting (hoisting) machines |
-
1979
- 1979-12-22 DE DE19792952053 patent/DE2952053A1/en not_active Withdrawn
-
1980
- 1980-12-04 GB GB8038950A patent/GB2066485B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2584218A1 (en) * | 1985-06-26 | 1987-01-02 | Fichet Bauche | Surveillance installation for areas to be protected |
| FR2731070A1 (en) * | 1995-02-28 | 1996-08-30 | Commissariat Energie Atomique | Position measurement by potentiometric sensors |
| RU2153678C2 (en) * | 1998-10-12 | 2000-07-27 | Открытое акционерное общество "Ракетно-космическая корпорация "Энергия" им. С.П. Королева" | Device for visual monitoring of voltage value |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2066485B (en) | 1983-06-22 |
| DE2952053A1 (en) | 1981-06-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |