CN201270088Y - RS-485 meter reading communication circuit - Google Patents

Abstract

The utility model discloses an RS-485 communication circuit for copying meter data which comprises an isolating power source system, a photoelectric isolating circuit, an RS-485 bus control chip, an RS-485 interface, an electric current transience inhibiting and voltage transience suppressing circuit, and a circuit with the combined functions of lightning protection, alternating current power source interlink prevention and overcurrent prevention, wherein, the circuit with the combined functions of lightning protection, alternating current power source interlink prevention and overcurrent prevention comprises two ceramic gassy discharging tubes that are respectively and parallelly connected with two signal wires and positioned at the input terminal of the RS-485 interface, thermal resistances that are respectively and serially connected with the two signal wires, and a solid discharging tube that is jumper connected between the two signal wires. The electric current transience inhibiting and voltage transience suppressing circuit comprises an electrical inductance and two resistances that are respectively and serially connected with the two signal wires, diodes that are respectively and parallelly connected with the two signal wires, and a TVS tube that is respectively and parallelly connected with the two signal wires. The RS-485 communication circuit for copying meter data has safe and reliable performance, and provides reliable guarantees for managing electric load and sampling electric energy data.

Description

The RS-485 telecommunication circuit of checking meter

Technical field

The utility model relates to a kind of RS-485 that is applied to the management of power load and data acquisition for electric energy terminal telecommunication circuit of checking meter.

Background technology

The RS-485 of the management of power load and data acquisition for electric energy terminal (hereinafter to be referred as " the terminal ") communication port of checking meter, be the base unit that terminal realizes data acquisition for electric energy, checking meter for terminal RS485, its safe reliability is very important the telecommunication circuit.Because the RS-485 communication network of terminal adopts twisted-pair feeder to make transmission line, transmission line is generally maked somebody a mere figurehead or is laid along cable duct outdoor on the one hand.On transmission line, cause the transition interference and damage device at thunderstorm season Chang Fashengyin thunder and lightning.And the RS-485 network topology adopts a bus that each node is connected in series usually, and the transition that thunder and lightning causes often causes a plurality of RS-485 transceivers on the transmission line to damage.Secondly, in terminal site operation and maintenance process, because construction or maintainer's carelessness may be gone into the RS-485 communication port with AC power (as the input of 220VAC alternating voltage) misconnection, thereby directly be caused terminal to damage.Simultaneously, in terminal operation process for a long time, because climatic environment is abominable, the RS-485 order wire can descend even short circuit (the exposed short circuit problem that causes with AC power of RS-485 order wire copper sheet for example to the insulating property of AC power; Or because there was dampness in the air, the provisional decline of the insulating property of RS-485 communication port and AC power), thus cause RS-485 communication port even terminal to be damaged.So it also is the terminal RS-485 problem that the telecommunication circuit design must deal carefully with of checking meter that anti-AC power inserts measure.In addition, the working condition very severe of terminal operating, especially, terminal, peripheral equipment is generally power equipment or forceful electric power device, and its electromagnetic interference (EMI) is very strong.According to portion of State Grid industry relevant criterion and various places terminal bid technical conditions, terminal climatic environment condition rank, the logical product of electromagnetic compatibility (EMC) testing requirements all are the strictest in each rank.For example: terminal climatic environment condition is the C3 rank, and the air themperature scope that then requires terminal to adapt to is-40～+ 70 ℃, and the relative humidity scope is 10%RH～100%RH.Pilot projects such as the esd immunity of terminal, high frequency interference, electrical fast transient (eft) immunity to interference, high-frequency sasser immunity to interference, surge immunity are all carried out requirement by wherein the strictest rank.Though consideration is in various degree also arranged in the problem prior art of above-mentioned 3 aspects, such as adopting insulating power supply system, RS-485 bus control chip, photoelectric isolating circuit etc., reliability is still not good enough, does not have overall above-mentioned solution.Therefore how could guarantee fully that the check meter safe reliability of telecommunication circuit of terminal RS-485 is still present problem demanding prompt solution.

The purpose of this utility model is to provide a kind of safe and reliable RS-485 that is used for the management of power load and data acquisition for electric energy terminal the telecommunication circuit of checking meter.

This RS-485 that the utility model the provides telecommunication circuit of checking meter comprises the insulating power supply system, photoelectric isolating circuit, RS-485 bus control chip, the RS-485 interface, RS-485 interface input end is by two signal wires and RS-485 bus control chip A, the B pin, it is characterized in that also having current transients inhibition voltage transient to clamp down on circuit in the prime of RS-485 bus control chip, the anti-AC power of lightning protection inserts the anti-overflow circuit, and wherein the anti-AC power access of lightning protection anti-overflow circuit comprises the two ceramic gaseous state discharge tube (V1 that are connected in parallel on described two signal wires respectively and are positioned at RS-485 interface input end, V2), be connected on the thermistor (F1 on described two signal wires respectively, F2), be connected across the solid-state discharge tube (V3) between described two signal wires; Described current transients suppress voltage transient clamp down on circuit comprise the inductance (L1, L2) that is connected on respectively on described two signal wires and two resistance (R1, R2), respectively be connected in parallel on diode (V4, V6, V5, V7) on described two signal wires, be connected in parallel on each TVS of one pipe (V8, V9) on described two signal wires.

RS-485 bus control chip of the present utility model and TVS pipe all adopts the antistatic protection function type.

From the technical solution of the utility model as can be seen; it has four layers of holding circuit; the ground floor holding circuit is that the anti-AC power of lightning protection inserts the anti-overflow circuit; when terminal runs into the thunderbolt interference; this circuit can be rapidly with the current potential clamper of RS-485 port A, B signal wire to normal level; and the discharge tube by the avalanche breakdown state, with the unnecessary interfering energy signal ground loop of releasing rapidly, reach the purpose of protection terminating circuit system.When the AC power situation is gone in the misconnection of RS-485 port; relevant holding circuit can produce corresponding actions; utilize the characteristic of thermistor heating under the big electric current promptly the AC power that inserts to be born; terminal inner weak current part and outside forceful electric power are intercepted to be opened; after the forceful electric power of the outside input of RS-485 port disappears; the protection action of interlock circuit is cancelled automatically, and circuit returns to normal operating conditions.Second layer holding circuit is that current transients inhibition voltage transient is clamped down on circuit; mainly solve the residual interference signal problem after big undesired signal is passed through the ground floor holding circuit; simultaneously; when RS-485 port input current potential surpasses normal amplitude (but this current potential does not also make discharge tube produce corresponding protection action); this layer of holding circuit also will be carried out the voltage clamp protection; make the RS-485 port in second layer holding circuit, its A, B signal wire current potential remain on the normal potential level.The three-layer protection circuit is actually and adopts the TVS pipe that possesses the esd protection function, and main effect is that transitions such as electrostatic prevention, pulse train are disturbed.Because after this layer holding circuit; undesired signal will directly be impacted RS-485 bus control chip; for guaranteeing that the design has more high reliability; so in the design of this layer holding circuit; the device that the TVS pipe should preferably design towards esd protection specially; require its responsiveness should be enough quick, prevent, cause the total line traffic control acp chip of RS-485 moment to be damaged because the device responsiveness is slow, the protection action response is not prompt enough.The 4th layer of holding circuit mainly is made up of insulating power supply system, RS-485 bus control chip and photoelectric isolating circuit, and in this layer holding circuit, RS-485 bus control chip should preferably self have the device of anti-esd protection.In addition,, the signal of communication of RS-485 port is isolated, guaranteed impact and harmful effect that the terminal inner circuit directly is not interfered by photoelectric isolating circuit.Above-mentioned four layers of protection make the performance of the utility model circuit safe and reliable, for the management of power load and data acquisition for electric energy provide reliable guarantee.

Description of drawings

Fig. 1 is a structured flowchart of the present utility model.

Fig. 2 is the circuit diagram of an embodiment of the utility model.

Embodiment

The utility model still has by insulating power supply system, RS-485 bus control chip and photoelectric isolating circuit and forms holding circuit as can be seen from Figure 1, also has esd protection circuit, current transients to suppress that voltage transient is clamped down on circuit, the anti-AC power of lightning protection inserts the anti-overflow circuit.

There are two signal wires to be connected at RS-485 interface input end as can be seen from Figure 2 with A, the B pin of RS-485 bus control chip, as ground floor holding circuit of the present utility model is that the anti-AC power of lightning protection inserts the anti-overflow circuit, and this circuit comprises two ceramic gaseous state discharge tube V1, the V2 that is connected in parallel on described two signal wires respectively and is positioned at RS-485 interface input end; Be connected on thermistor F1, F2 on described two signal wires respectively; Be connected across the solid-state discharge tube V3 between described two signal wires, second layer holding circuit is that current transients inhibition voltage transient is clamped down on circuit, and this circuit comprises inductance L 1, L2 and two resistance R 1, the R2 that is connected on respectively on described two signal wires; Be connected in parallel on the diode (V4, V6, V5, V7) on described two signal wires respectively; Be connected in parallel on described two signal wires each TVS of one pipe (V8, V9), wherein diode V4, V6 respectively with described two signal wires in one in parallel, diode V5, V7 are in parallel with another root respectively.The model that ceramic in the present embodiment gaseous state discharge tube V1, V2 use is ARR-AM470L-CA8, and its dc breakdown voltage is 470V, the 10kA of anti-the short-circuit current.It is LGA0410-102K that inductance L 1, L2 adopt model, and it is the two-way TVS pipe SMBJ10CA of 10V that two TVS pipe V8, V9 adopt clamp voltage.

The lightning protection design mainly is two ceramic gaseous state discharge tube V1, V2.When the protection action takes place in these two gaseous state discharge tubes; can shift most transient energy rapidly; and,, be particularly suitable for absorbing direct lightning strike and respond to the huge interfering energy that thunder causes so its discharge capacity is very big because it does not have distributed inductance or electric capacity.But, the movement response time of gaseous state discharge tube relatively slow (≤100ns), so the residual voltage and the transient current that have still that amplitude reaches or surpass 20V seal in late-class circuit.If it is that (annotate: long-time thunderbolt is defined as electric current and is longer than 2ms from wave head from the time that peak value 10% to wave rear is reduced between the peak value 10%, and is shorter than the thunderbolt of 1s in long-time thunderbolt that outside thunderbolt is disturbed.), even repeatedly thunderbolt for a long time, this long-term residual voltage will cause the direct damage of RS-485 bus control chip so.So, to further protect processing in the subsequent conditioning circuit.

When A, the B two ends of RS-485 interface are gone in the AC power misconnection, the holding circuit of forming by solid-state discharge tube V3, diode V4, V5, V6, V7 then moment with the voltage clamp between A, the B two ends between-0.7V～5.7V; And then by TVS pipe V8, V9 (actuation time≤1ns), the common mode between A, the B two ends, differential mode voltage are carried out over-voltage clamping.If the electric current by thermistor F1, F2 has reached or surpass the action current of this device, thermistor will move rapidly, and its resistance value can be had to go to the toilet to increase severely and be added short time.Like this, the pressure drop of most of AC power all is split on the thermistor, thereby subsequent conditioning circuit and external communication forceful electric power are isolated.After external ac power source disappeared, it is normal that the resistance value of thermistor F1, F2 can be recovered voluntarily.

Current transients suppresses voltage transient, and to clamp down on circuit design be to utilize the principle that electric current can not suddenly change on the inductance L 1 that is connected on described two signal wires, its inductance of L2; electric current is carried out the transition inhibiting effect; also for more follow-up protection gains time, and alleviate pressure to follow-up holding circuit.And solid-state discharge tube V3, diode V4, V5, V6, V7, TVS pipe V8, V9 are further protections.Wherein, V4, V5, V6, V7 employing rated current are the diode S1M of 1A; It is the two-way TVS pipe SMBJ10CA of 10V that V8, V9 adopt clamp voltage.Their main effect be the RS-485 bus potential is controlled at-0.7V～5.7V between, its subsequent conditioning circuit just is operated in the normal voltage scope like this.

It is esd protection that design is disturbed in transition such as electrostatic prevention, pulse train, owing to static, pulse train disturb the speed that produces, discharges very fast.For example, electrostatic interference is finished the overall process that bursts out to disappearing usually in several nanoseconds (ns).Though static, pulse train disturb the energy that is discharged also little, its crest voltage is considerably beyond the absolute rating of most of semi-conductor chip or device, so often can cause damage to semi-conductor chip or device.The measure that the utility model is taked is that TVS pipe and RS-485 bus control chip have all adopted the antistatic protection function type; V8, V9 adopt SMBJ10CA as the TVS pipe; but its moment (less than 1ns) about 20V, is played once protection with the voltage clamp between the RS-485 bus.485 communication interface chips adopt the SN65LBC184 with electrostatic-proof function, and it can bear ± 30KV contact discharge (IEC61000-4-2), ± 15KV atmospherical discharges (IEC61000-4-2).SN65LBC184 plays protective effect once more like this.By photoelectric isolating circuit, the signal of communication of RS-485 port is isolated then, guaranteed impact and harmful effect that the terminal inner circuit directly is not interfered.

Claims (4)

1, a kind of RS-485 telecommunication circuit of checking meter, comprise the insulating power supply system, photoelectric isolating circuit, RS-485 bus control chip, the RS-485 interface, RS-485 interface input end is by the A of two signal wires and RS-485 bus control chip, the B pin connects, it is characterized in that also having current transients inhibition voltage transient to clamp down on circuit in the prime of RS-485 bus control chip, the anti-AC power of lightning protection inserts the anti-overflow circuit, and wherein the anti-AC power access of lightning protection anti-overflow circuit comprises the two ceramic gaseous state discharge tube (V1 that are connected in parallel on described two signal wires respectively and are positioned at RS-485 interface input end, V2), be connected on the thermistor (F1 on described two signal wires respectively, F2), be connected across the solid-state discharge tube (V3) between described two signal wires; Described current transients suppress voltage transient clamp down on circuit comprise the inductance (L1, L2) that is connected on respectively on described two signal wires and two resistance (R1, R2), respectively be connected in parallel on diode (V4, V6, V5, V7) on described two signal wires, be connected in parallel on each TVS of one pipe (V8, V9) on described two signal wires.

2, the RS-485 according to claim 1 telecommunication circuit of checking meter is characterized in that TVS pipe and RS-485 bus control chip all adopt the antistatic protection function type.

3, the RS-485 according to claim 2 telecommunication circuit of checking meter is characterized in that the model that the TVS pipe adopts is SMBJ10CA.

4, the RS-485 according to claim 2 telecommunication circuit of checking meter is characterized in that the model that RS-485 bus control chip adopts is SN65LBC184.

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