EP4227974A1 - Verfahren und elektronische schaltung zur relaisbestandsdetektion - Google Patents

Verfahren und elektronische schaltung zur relaisbestandsdetektion Download PDF

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Publication number
EP4227974A1
EP4227974A1 EP22155770.5A EP22155770A EP4227974A1 EP 4227974 A1 EP4227974 A1 EP 4227974A1 EP 22155770 A EP22155770 A EP 22155770A EP 4227974 A1 EP4227974 A1 EP 4227974A1
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EP
European Patent Office
Prior art keywords
relay
peak
time
derivative
monitored
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
Application number
EP22155770.5A
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English (en)
French (fr)
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EP4227974B1 (de
Inventor
Peter SPISÁK
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BSH Hausgeraete GmbH
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BSH Hausgeraete GmbH
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Priority to EP22155770.5A priority Critical patent/EP4227974B1/de
Publication of EP4227974A1 publication Critical patent/EP4227974A1/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/002—Monitoring or fail-safe circuits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/002—Monitoring or fail-safe circuits
    • H01H47/004—Monitoring or fail-safe circuits using plural redundant serial connected relay operated contacts in controlled circuit
    • H01H47/005—Safety control circuits therefor, e.g. chain of relays mutually monitoring each other
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H3/00—Mechanisms for operating contacts
    • H01H3/001—Means for preventing or breaking contact-welding

Definitions

  • the invention refers to a method enabling a detection if a relay is stuck, an electric circuit adapted to run the method, and an electric household appliance.
  • a malfunction of a relay is determined, especially if the relay switches high current load.
  • An example for a malfunction is a relay that is stuck after it has been switched off.
  • the relay When working normally, as soon as the relay is switched OFF (i.e. the current coil is switched OFF), the armature moves fully back to its relaxed position (open state). This backwards movement is caused by spring power, mostly by two springs, a return spring and a contact compression spring. In addition, when working normally, the armature starts moving backwards delayed after the relay has been switched OFF. The reason for the delay is the fact that the magnetic force has to collapse below a certain level in order to release the anchor. However, sometimes the relay does not open properly, due to various reasons such that the anchor is stuck to the coil.
  • the relay 1 consists of a static coil 2 and an armature having the following major parts: anchor mechanics 4, anchor return spring (not shown), contact compression spring 6 and movable electric contact 8.
  • the relay has three basic anchor/contact positions.
  • FIG 1a the relay 1 is shown in its normally open state (NO).
  • NO normally open state
  • the coil 2 is not energised and the anchor 4 has not been pulled towards the coil 2.
  • the relay 1b the relay 1 is shown in its transition state. In this state, the coil 2 is energised and a magnetic force is built up such that the anchor 4 is slightly pulled towards the coil 2.
  • relays with a reinforced insulation may have a lever mechanism made from insulated material placed between the anchor and movable contact parts.
  • These mechanisms can be in the form of a push-pull-mechanism, adapted to move the movable contact in both directions (ON and OFF).
  • a push-mechanism can be provided, adapted to move the movable contact in push direction (ON) only.
  • the push-pull mechanism may have some movement clearance between anchor and movable contact compression spring, or may even feature some mechanical clearance hysteresis.
  • a method for relay stuck detection comprises the steps:
  • the stuck relay detection works on the low voltage side by detecting if there is a change in a 3 rd derivative peak of the I(t) curve outside a given tolerance, which appears at the time of an expected time when the relay contact switches OFF.
  • the negative peak value is taken into account.
  • the switch OFF time is the interval or period of time between a de-energizing of the relay coil to switch OFF normally open (NO) relay contact and time point when the relay contacts release their touch. This is notably the time between two large negative peaks on 3rd derivative peaks.
  • a comparison between a second peak on the 3 rd differential curve and a second stored peak value representing a part of the switch OFF behaviour of the standard relay is taken into account for the evaluation. This can be the case if the detected first peak has an amplitude (negative amplitude) that is similar than the amplitude (negative amplitude) of the first stored peak directly after the relay has been switched OFF. At first sight, it seems that the detected relay works well, as a first 3 rd derivative peak having a high amplitude appears when the contacts lose their contact. However, in order to review this, a second peak value is detected and compared with stored second peak value.
  • a calculated time difference between the detected first peak and the detected second peak of the monitored relay is compared with a stored time difference between the stored first peak and the stored second peak and taken into account for the evaluation.
  • the switch OFF time can also indicate a possible relay failure, but preferably, the time difference is not sufficient to confirm if the relay is stuck.
  • the inventive method follows the following workflow during its switch OFF procedure:
  • an expected relay switching OFF time confirms the positive peak on 1 st derivative I(t) curve.
  • the expected relay switch OFF time for stuck relay can be shorter, untouched or even longer than that for normally working relay. If the relay armature is not movable due to stuck contacts for instance, said derivative peaks disappear at all.
  • the workflow according to the invention works well for relays with relay armature firmly connected to movable contact and its compression spring and for push-pull type armature relays with low mechanical clearance and/or mechanical hysteresis.
  • the details of electrical voltage/current values of I(t) curve, its derivatives and particular peaks respectively are relay type specific and should be adjusted and pre-memorized for relay types used to define status of normally working relay.
  • the proposed stuck relay detection technique can be used as standalone feature or as an add-on feature if the appliance already uses zero cross relay switching technique as exemplary described in WO 2020/020555 A1 of the applicant. Both the techniques can form very powerful tool to switch the appliance relays, to monitor and predict their health status and to detect possible failure of relay switching contacts. All the control and detection is made solely on relay low voltage side without any measurement or controlling on its high voltage side.
  • an electronic circuit adapted to relay stuck detection comprises a relay having a coil to be monitored and three subsequent differentiators in series each calculating one derivative of the relay coil current over the time I(t), wherein between the first differentiator and the second differentiator a low pass filter is provided and wherein the output signal of the first differentiator and the output signal of the second differentiator is amplified by a first amplifier and by a second amplified, respectively.
  • the differentiators reliable enable to calculate the 3 rd derivate according to the inventive method.
  • the low pass filter eliminates efficiently higher interferences frequencies.
  • a flyback diode can be provided in parallel to the relay coil.
  • a resistor provided for measuring a voltage can be positioned in series with the relay coil.
  • a resistor is positioned in series with the flyback diode in order to pick-up the relay current I(t) of the monitored relay.
  • an electric household appliance comprises an inventive electric circuit.
  • Such a household appliance fulfils a high electric safety standard as any malfunction of a relay will be detected easy and reliable.
  • Figure 2a shows a I(t) pattern 12 when switching OFF a relay 1 with normally movable NO contact.
  • the second and third derivatives 18, 20 are uncompensated for slight time delays coming from time constants of each differentiator circuits. Each curve peaks are relative in their measures, controllable by differentiator electronics to facilitate the detection.
  • Figure 2a shows an isolated 3 rd derivate curve 20 of the relay 1.
  • the exact time of the relay switch OFF defines the middle of positive peak on the first derivate curve 16. It should be noted that this time point does not fit with time point of a local positive peak at the I(t) curve 14, it happens a bit earlier. Irregularities shown in the current I(t) curve 14 are based on from mechanical dynamics of the relay armature.
  • the relay moving contact In the event the relay moving contact is stuck, the relay armature is exposed to a sudden, sharp jerk, when trying to move during the switch OFF procedure. This is detectable by a peak 24 on the third derivative curve 20 and appears at the expected time of contact touch releasing. If the contact is normally movable, the expected peak 24 at a second breakpoint should be rather small. The reason for the peak 24 is a sudden mass addition due to the moving of the armature parts. If the movable contact is stuck, for instance welded together with static contact part, the moving armature is subjected to a sudden strike, when trying to peel it off, to release it from static contact part. This state can be detected by the large peak 24 on the d 3 l/dt 3 curve appearing at a time of expected contact touch releasing.
  • the principle of stuck relay detection is to detect a significant change in the 3 rd derivative peaks 24, which appears at the time of expected time t2 when the relay contact switches OFF.
  • Each relay has following key parameters, which may be relay type specific:
  • a 3 rd derivate of coil current I(t) of a normal working relay ( figure 3 ) and of a monitored relay ( figure 4 ) is given.
  • a high first negative peak 22 and a low second negative peak 24 after a specific period of time (t1 - t2) are clearly detectable.
  • the specific period of time is the switch-OFF time of the relay.
  • both curves 20, 26 shows high first negative peaks 22, 28 at the beginning of the switch-OFF time.
  • second peaks 24, 30 on both third derivate curves 20, 26 are detected and compared regarding their (negative) amplitude and their time difference (t1 - t2) measured from the appearance of the first peaks 22, 26 to the appearance of the second peaks 24, 30.
  • the second negative peak value 30 of the monitored relay appears earlier and has a higher negative value than the stored second peak 24 of the normal working relay. Both the smaller time difference (t1 - t2) and the higher amplitude give a hint to a misfunction of the monitored relay.
  • the movable contact can be stuck also in a position beyond its standard fully closed state. This may happen due to scattering (removing) part of relay contact material in course of relay ageing.
  • the I(t) curve 32 is similar to a standard exponential I(t) curve observed at an electromagnetic coil with fixed inductance. There are no significant first peaks on any of said derivative curves 36, 38, 40. In particular, there is only a small first negative peak 34 on the 3 rd derivate curve 40 and no second peak 42 on the 3 rd derivative curve at the expected relay switch OFF time at all.
  • a preferable analogue circuit diagram to generate 1 st , 2 nd , and 3 rd derivatives of an I(t) curve by three-step C-R differentiator 42 is given.
  • the electronic circuit 42 is adapted to relay stuck detection, comprising a relay L1 having a coil to be monitored and three subsequent differentiators C1, R3; C3, R6 and C4, R9 in series, each calculating one derivative of the relay coil current over the time I(t).
  • a low pass filter R2, C2, R5, R4 is provided between the first differentiator C1, R3 and the second differentiator C3, R6 a low pass filter R2, C2, R5, R4 is provided.
  • the output signal of the first differentiator C1, R3 and the output signal of the second differentiator C3, R6 is amplified by a first amplifier U1 and by a second amplifier U2, respectively.
  • the first C-R differentiator step includes R1, R2, C1, R3, U1, C2, R4, R5.
  • An I(t) curve pick-up technique is to pick up the voltage from a measuring resistor which is connected in series to the relay coil, or in series to the relay flyback diode D1 (diode suppressing inductive voltage peaks when switching the relay).
  • a measuring resistor which is connected in series to the relay coil, or in series to the relay flyback diode D1 (diode suppressing inductive voltage peaks when switching the relay).
  • flyback diode D1 diode suppressing inductive voltage peaks when switching the relay.
  • Figure 7 is a detailed view 44 of figure 6 and shows a basic schematic representation for picking up the I(t) curve and converting it into voltage.
  • a resistor R1 provided for measuring a voltage in order to pick-up the relay current I(t) of the monitored relay L1 is in series with the relay coil.
  • FIG 8 an alternative 46 to the embodiment shown in figure 7 is illustrated.
  • the resistor R1 provided for measuring the voltage in order to pick-up the relay current I(t) of the monitored relay L1 is positioned in series with the flyback diode D1.
  • the I(t) curve is picked up in both cases; when switching the relay L1 ON and OFF. If the resistor R1 is incorporated in the flyback diode circuit (flyback diode D1), picking-up is possible only for the switch OFF procedure. In this case, the resistor R1 does not lower the voltage on the relay L1 during its switching ON procedure.

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  • Relay Circuits (AREA)
EP22155770.5A 2022-02-09 2022-02-09 Verfahren und elektronische schaltung zur relaisbestandsdetektion Active EP4227974B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP22155770.5A EP4227974B1 (de) 2022-02-09 2022-02-09 Verfahren und elektronische schaltung zur relaisbestandsdetektion

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EP22155770.5A EP4227974B1 (de) 2022-02-09 2022-02-09 Verfahren und elektronische schaltung zur relaisbestandsdetektion

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EP4227974A1 true EP4227974A1 (de) 2023-08-16
EP4227974B1 EP4227974B1 (de) 2024-11-06

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017055031A1 (de) * 2015-10-02 2017-04-06 BSH Hausgeräte GmbH Haushaltsgerät
WO2020020555A1 (en) 2018-07-24 2020-01-30 BSH Hausgeräte GmbH Method and control unit for switching on or off a relay
DE102020207276A1 (de) * 2020-06-10 2021-12-16 BSH Hausgeräte GmbH Verfahren und Steuereinheit zum Schalten eines Relais bei Nulldurchgang

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017055031A1 (de) * 2015-10-02 2017-04-06 BSH Hausgeräte GmbH Haushaltsgerät
WO2020020555A1 (en) 2018-07-24 2020-01-30 BSH Hausgeräte GmbH Method and control unit for switching on or off a relay
DE102020207276A1 (de) * 2020-06-10 2021-12-16 BSH Hausgeräte GmbH Verfahren und Steuereinheit zum Schalten eines Relais bei Nulldurchgang

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