CN209894874U - Residual current sampling conditioning circuit - Google Patents
Residual current sampling conditioning circuit Download PDFInfo
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- CN209894874U CN209894874U CN201920356893.1U CN201920356893U CN209894874U CN 209894874 U CN209894874 U CN 209894874U CN 201920356893 U CN201920356893 U CN 201920356893U CN 209894874 U CN209894874 U CN 209894874U
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Abstract
The utility model discloses a residual current sampling conditioning circuit, which comprises a signal sampling circuit, wherein the signal sampling circuit is connected with the output end of a residual current transformer; the output end of the signal sampling circuit is connected with a dual-channel signal conditioning circuit with different amplification factors in series, and the front end of the dual-channel signal conditioning circuit is connected with a bias voltage circuit in series; the dual-channel signal conditioning circuit comprises a low-gain channel U8C and a high-gain channel U9B which are connected in parallel; the low-gain channel U8C conditions the large-current signal; the high gain path U9B conditions the low current signal. The utility model adopts the double-channel signal conditioning circuit with different amplification factors, and the low-gain channel conditions the heavy current signal; the high gain channel conditions the low current signal. The current detection range of the detector is enlarged, the residual current in a wider range can be detected, the measurement of small current and large current is considered, and the precision of sampling current is ensured.
Description
Technical Field
The utility model relates to a sampling circuit, concretely relates to residual current sampling conditioning circuit.
Background
The residual current transformer is a group of coils wound on a high-permeability material, and is generally provided with a metal shielding layer in order to prevent external interference. The residual current transformer is a straight-through transformer, and a protected circuit needs to completely penetrate through the residual current transformer when the residual current transformer is used. Under normal conditions, because of current balance, the vector sum of the primary sides is zero, and the output of the residual current transformer is zero; when leakage fault and earth fault occur, the vector sum is not zero, and the residual current outputs a current signal which is in direct proportion to the vector sum.
In the existing residual current protector, only one channel is used for carrying out signal acquisition on residual current by a detector, so that the measuring range of the detector is small, the error is large, and the consistency of the residual current protection action characteristic cannot be ensured.
Disclosure of Invention
In view of the above technical problems, the present technical solution provides a residual current sampling and conditioning circuit, which can effectively solve the above problems.
The utility model discloses a following technical scheme realizes:
a residual current sampling conditioning circuit comprises a signal sampling circuit, wherein the signal sampling circuit is connected with the output end of a residual current transformer; the output end of the signal sampling circuit is connected with a dual-channel signal conditioning circuit with different amplification factors in series, and the front end of the dual-channel signal conditioning circuit is connected with a bias voltage circuit in series; the dual-channel signal conditioning circuit comprises a low-gain channel and a high-gain channel which are connected in parallel; the low-gain channel conditions a large-current signal; the high gain channel conditions the low current signal.
Furthermore, the low-gain channel is an inverting amplification circuit composed of an operational amplifier U8C and a peripheral circuit, the inverting input end of the operational amplifier U8C is connected with a current-limiting resistor R86, and a feedback resistor R85 is connected between the inverting input end and the output of the operational amplifier U8C;
the high-gain channel is an inverse amplification circuit consisting of an operational amplifier U9B and a peripheral circuit, the inverting input end of the operational amplifier U9B is connected with a current-limiting resistor R96, and a feedback resistor R95 is connected between the inverting input end and the output of the operational amplifier U9B.
Further, the amplification factor of the low-gain channel is the resistance ratio of the feedback resistor R85 to the current-limiting resistor R86, and the ratio of the amplification factor to the current-limiting resistor R86 is 1: 1; the amplification factor of the high-gain channel is the resistance ratio of the feedback resistor R95 to the current-limiting resistor R96, and the ratio is 5: 1.
Further, the operational amplifier U8C and the operational amplifier U9B adopt an LMV324 four-way low-voltage rail-to-rail output operational amplifier; the power supply is supplied by a single-phase direct current 3.3V power supply.
Furthermore, a protection diode is connected in the dual-channel signal conditioning circuit.
Furthermore, the signal sampling circuit is composed of a sampling resistor R88 and a filter capacitor C70, and the sampling resistor R88 is connected between the output ends of the residual current transformer in a bridge mode.
Furthermore, the signal sampling circuit converts the residual current signal output by the output end of the residual current transformer into a voltage signal in an equal proportion.
Furthermore, after the residual current signal is processed by the signal sampling circuit, the relation between the voltage amplitude and the residual current is 360mV/1000 mA.
Furthermore, the bias voltage circuit reduces the voltage provided by the voltage-stabilized power supply by a half proportion and then supplies the voltage to the dual-channel signal conditioning circuit.
Furthermore, a voltage division circuit is connected in the bias voltage circuit, the input end of the voltage division circuit is connected with a stabilized voltage power supply, and the output end of the voltage division circuit is connected with an operational amplifier U8A.
Furthermore, the voltage division circuit divides the voltage of the stabilized voltage power supply by a half ratio and then outputs the voltage to be connected with the positive input end of the operational amplifier U8A.
Further, the voltage-stabilized power supply is 3.3V, and the voltage-dividing circuit divides the voltage of the 3.3V voltage-stabilized power supply and outputs 1.65V voltage.
Further, the inverting input terminal and the output terminal of the operational amplifier U8A are connected to form a voltage follower.
Advantageous effects
The utility model provides a pair of residual current sampling conditioning circuit compares with prior art, and it has following beneficial effect:
(1) the circuit adopts a dual-channel signal conditioning circuit with different amplification factors, wherein the dual-channel signal conditioning circuit comprises a low-gain channel and a high-gain channel which are connected in parallel; the low-gain channel conditions a large-current signal; the high gain channel conditions the low current signal. The current measuring range of the detector is enlarged, the measurement of small current and large current is considered, the precision of sampling current is guaranteed, and meanwhile the consistency of the action characteristics of the residual current protector is guaranteed.
(2) The arrangement of the protective diode can prevent the operational amplifier or other circuits in the dual-channel signal conditioning circuit from being damaged due to overhigh voltage of the input signal, and the circuit is protected.
(3) After the input voltage is subjected to voltage division by a voltage division circuit, buffering and isolating the voltage of 1.65V obtained after voltage division by a voltage follower, and then outputting the voltage; the load capacity of the voltage is improved.
(4) The design of the voltage stabilizing filter circuit ensures that the bias voltage entering the divider resistor is more stable, and plays an auxiliary role in collecting more accurate voltage for the voltage sampling circuit.
Drawings
Fig. 1 is a schematic circuit connection diagram of the overall structure of the present invention.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are only some, but not all embodiments of the invention. Under the prerequisite that does not deviate from the design concept of the utility model, the ordinary person in the art should fall into the protection scope of the utility model to the various changes and improvements that the technical scheme of the utility model made.
Example (b):
as shown in fig. 1, a residual current sampling and conditioning circuit includes a signal sampling circuit, where the signal sampling circuit is connected with an output end of a residual current transformer; the output end of the signal sampling circuit is connected with a dual-channel signal conditioning circuit with different amplification factors in series, and the front end of the dual-channel signal conditioning circuit is connected with a bias voltage circuit in series.
The signal sampling circuit comprises a sampling resistor R88 and a filter capacitor C70, and the sampling resistor R88 is connected between the output ends of the residual current transformer in a bridge mode. The signal sampling circuit converts the residual current signals output by the output end of the residual current transformer into voltage signals in equal proportion. In this embodiment, the residual current transformer is a model SY3.572.001 residual current transformer, and the output current ratio is 1000: 1, 1000mA output current is 1 mA; in this embodiment, the resistance of the sampling resistor R88 is 360 ohms, and the resistance of the sampling resistor R88 is substituted into the formula of U = I × R, where U =1 × 360=360 mV; and setting the residual current to 360mV after passing through the signal acquisition circuit. After the residual current signal is processed by the signal sampling circuit, the relation between the voltage amplitude and the residual current is 360mV/1000 mA.
The dual-channel signal conditioning circuit comprises a low-gain channel and a high-gain channel which are connected in parallel;
the low-gain channel is an inverse amplification circuit consisting of an operational amplifier U8C and a peripheral circuit, and the inverting input end of the operational amplifier U8C is connected with a current-limiting resistor R86; a feedback resistor R85 is connected between the inverting input end and the output of the operational amplifier U8C, and a filter capacitor C67 is connected in parallel to the feedback resistor R85. The non-inverting input terminal of the operational amplifier U8C is connected to a bias voltage, which converts the voltage to 1.65V and then is connected to the non-inverting input terminal of the operational amplifier U8C through a parallel filter capacitor C69. The amplification factor of the low-gain channel is the ratio of the resistance of the resistor R85 to the resistance of the resistor R86, and the ratio is 1: 1. In this embodiment, the feedback resistor R85 has a resistance of 2K, and the current limiting resistor R86 has a resistance of 2K.
The high-gain channel is an inverse amplification circuit consisting of an operational amplifier U9B and a peripheral circuit, the inverting input end of the operational amplifier U9B is connected with a current-limiting resistor R96, and a feedback resistor R95 is connected between the inverting input end and the output of the operational amplifier U9B; the feedback resistor R95 is connected in parallel with a filter capacitor C75. The non-inverting input of the operational amplifier U9B is connected to a bias voltage, which converts the voltage to 1.65V and then directly connected to the non-inverting input of the operational amplifier U9B. The amplification factor of the high-gain channel is the resistance ratio of the feedback resistor R95 to the current-limiting resistor R96, and the ratio is 5: 1. In this embodiment, the feedback resistor R95 has a resistance of 10K, and the current limiting resistor R86 has a resistance of 2K.
In the present embodiment, the operational amplifier U8C and the operational amplifier U9B are LMV324 four-way low voltage rail-to-rail output operational amplifiers; the power supply is supplied by a single-phase direct-current stabilized power supply of 3.3V.
In order to prevent the operational amplifier or other circuits from being damaged due to the fact that the voltage of an input signal is too high, diodes such as D48, D46 and D47 are added in the dual-channel signal conditioning circuit to serve as protection.
The bias voltage circuit reduces the voltage provided by the voltage-stabilized power supply by a half proportion and then supplies the voltage to the dual-channel signal conditioning circuit. The bias voltage circuit is composed of U8A, R64, R71 and C34. Wherein, R64, R71 form the bleeder circuit, output after obtaining 1.65V with the voltage-stabilizing power voltage division of 3.3V, connect with the positive input end of the operational amplifier U8A; c34 is a filter capacitor for filtering interference signals; the inverting input and output of operational amplifier U8A are connected to form a voltage follower. The voltage of 1.65V is output after passing through the voltage follower and is connected with the low-gain channel and the high-gain channel.
The working principle is as follows: after a sampling resistor R88 in the signal sampling circuit collects a current signal output by the residual current transformer, the residual current signal output by the output end of the residual current transformer is converted into a voltage signal in equal proportion. After the residual current signal is processed by the signal sampling circuit, the relation between the voltage amplitude and the residual current is 360mV/1000 mA.
The low-gain channel conditions a large-current signal; when the residual current is 2000mA, the residual current enters a low-gain channel U8C through a current-limiting resistor R86 to be conditioned, the residual current is amplified by 1 time, the residual current 2000mA is brought into the following formula, and the solving formula is as follows:
Ui=(I/In)*Ue
in the above formula, I is the current residual current value, In is the rated current value (1000mA), and Ue is the voltage value (360mV) corresponding to the rated current value.
Uin = (2000/1000) × 0.36= 0.72V; multiplying the solved voltage by Uout = Uin 1=0.72V of the amplification factor; and outputting a conditioned signal after conditioning, wherein the voltage of the conditioned signal is 0.72V.
Conditioning the low current signal according to the high gain channel; when the residual current is 400mA, the residual current enters a high-gain channel U8C through a current-limiting resistor R96 to be conditioned, the residual current is amplified by 5 times, the residual current 400mA is brought into the following formula, and the solving formula is as follows:
Ui=(I/In)*Ue
in the above formula, I is the current residual current value, In is the rated current value (1000mA), and Ue is the voltage value (360mV) corresponding to the rated current value;
uin = (400/1000) × 0.36= 0.144V; multiplying the solved voltage by Uout = Uin × 5=0.72V of the amplification factor; and outputting a conditioned signal after conditioning, wherein the voltage of the conditioned signal is 0.72V.
Claims (10)
1. A residual current sampling conditioning circuit comprises a signal sampling circuit, wherein the signal sampling circuit is connected with the output end of a residual current transformer; the method is characterized in that: the output end of the signal sampling circuit is connected with a dual-channel signal conditioning circuit with different amplification factors in series, and the front end of the dual-channel signal conditioning circuit is connected with a bias voltage circuit in series; the dual-channel signal conditioning circuit comprises a low-gain channel and a high-gain channel which are connected in parallel; the low-gain channel conditions a large-current signal; the high gain channel conditions the low current signal.
2. The residual current sampling conditioning circuit of claim 1, wherein: the low-gain channel is an inverse amplification circuit consisting of an operational amplifier U8C and a peripheral circuit, the inverting input end of the operational amplifier U8C is connected with a current-limiting resistor R86, and a feedback resistor R85 is connected between the inverting input end and the output of the operational amplifier U8C;
the high-gain channel is an inverse amplification circuit consisting of an operational amplifier U9B and a peripheral circuit, the inverting input end of the operational amplifier U9B is connected with a current-limiting resistor R96, and a feedback resistor R95 is connected between the inverting input end and the output of the operational amplifier U9B.
3. The residual current sampling conditioning circuit of claim 2, wherein: the amplification factor of the low-gain channel is the resistance ratio of the feedback resistor R85 to the current-limiting resistor R86, and the ratio of the amplification factor to the current-limiting resistor R86 is 1: 1; the amplification factor of the high-gain channel is the resistance ratio of the feedback resistor R95 to the current-limiting resistor R96, and the ratio is 5: 1.
4. The residual current sampling conditioning circuit of claim 2, wherein: the operational amplifier U8C and the operational amplifier U9B adopt LMV324 four-way low-voltage rail-to-rail output operational amplifiers; the power supply is supplied by a single-phase direct current 3.3V power supply.
5. The residual current sampling conditioning circuit of claim 1, wherein: the signal sampling circuit is composed of a sampling resistor R88 and a filter capacitor C70, and the sampling resistor R88 is connected between the output ends of the residual current transformer in a bridging mode.
6. A residual current sampling conditioning circuit according to any one of claims 1 or 5, wherein: the signal sampling circuit converts the residual current signals output by the output end of the residual current transformer into voltage signals in equal proportion.
7. The residual current sampling conditioning circuit of claim 6, wherein: after the residual current signal is processed by the signal sampling circuit, the relation between the voltage amplitude and the residual current is 360mV/1000 mA.
8. The residual current sampling conditioning circuit of claim 1, wherein: the bias voltage circuit reduces the voltage provided by the voltage-stabilized power supply by a half proportion and then supplies the voltage to the dual-channel signal conditioning circuit.
9. A residual current sampling conditioning circuit according to any one of claims 1 or 8, wherein: the bias voltage circuit is connected with a voltage division circuit, the input end of the voltage division circuit is connected with a voltage-stabilized power supply, and the output end of the voltage division circuit is connected with an operational amplifier U8A.
10. The residual current sampling conditioning circuit of claim 9, wherein: and the inverting input end and the inverting output end of the operational amplifier U8A are connected to form a voltage follower.
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| CN201920356893.1U CN209894874U (en) | 2019-03-20 | 2019-03-20 | Residual current sampling conditioning circuit |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111721983A (en) * | 2020-06-23 | 2020-09-29 | 广东电网有限责任公司 | Current measurement clamp meter |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111721983A (en) * | 2020-06-23 | 2020-09-29 | 广东电网有限责任公司 | Current measurement clamp meter |
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