IEC_1107_Electricity_Meter_Interface.pdf

TEST&MEASUREMENT32Elektor Electronics3/20021Editors note:Some IEC1107 compliant elec-tricity meters used in the UK and other Euro-pean countries may have password protec-tion.The software referred to in thisarticle does not make provision forpasswords to be entered.(Ed.)Among its prodigious output of doc-uments describing internationalelectrical standards the InternationalElectrotechnical Commission(IEC)produced a specification IEC 1107that defines a software communica-tion protocol and the hardware nec-essary to pass information to andfrom electronic meters used to mea-sure such things as electricity,gasand water consumption in the homeand industry.Practically all the con-sumer meters manufactured thesedays have a microprocessor lurkingsomewhere inside and most areequipped with an IEC 1107 compli-ant interface or the equivalent Euro-pean spec EN61107.The opticalinterface was originally introducedby the companies Ferranti and Lan-dis&Gyr hence is alternative name,the FLAG port,derived from thecompany initials.This interface sim-plifies many functions of the meteroperation and here in the UK it ispossible for an operator from theelectricity company to reset internalregisters,alter the meter configura-tion and change tariffs via this inter-face.Before you get too excited Ithink we should point out that allIEC 1107Electricity Meter Interfacetalk to your electricity meterBy C.MesterMany electricity meters installed since the mid 1980s are equipped withan IEC1107 compliant optical interface.This gives a convenient method forthe Electricity Company to access all manner of information held in themeter using a hand terminal.This simple project describes a neat IEC1107to RS232 interface that together with some software allows a PC to talkto the meter and retrieve energy consumption information1.K1DB9123456789D11N4148D2D3D41N4148D5D6C210C110R4390D8SFH4853x3xR2100kR1100kD7BPW43236IC174741P220kP1000195-11Figure 1.The ultra-simple interface circuit.Power for the transmitting diode is provideddirectly from the TXD signal.An Opamp comparator is used to amplify the received signal.TEST&MEASUREMENT333/2002Elektor Electronicstial divider chain formed by R1 and R2 setsthe voltage at the inverting input to IC1.Infrared receiving diode D7 is connected inparallel to R1 so that IR light falling on D7 willeffectively reduce the resistance of the R1/D7pair and so produce a waveform at the inputto IC1 which corresponds to the received IRsignal.The signal is converted to RS232 volt-age levels by IC1 so that the output signal canbe used to drive the received data line(RXD)directly.Signals to the meter are produced bythe infrared emitting diode D8 while R4 limitsthe forward conduction current.The data rate defined in the IEC 1107 pro-tocol is so low that a standard 741 type op-amp is also suitable for use as a comparatorin this application.The layout of the circuit is so simple anduncritical that even without a purpose-madePCB construction should present few prob-lems.The only points to look out for are firstlyto ensure that you use a 9-way D-type socketfor connector K1 and not a plug and also thatthe receiving diode D7 is fitted with a hood ortube so that it can only detect light comingfrom directly in front of it.If you choose tomount D7 any distance from the rest of theinterface circuitry then the cabling to D7should be screened.Circuit alignment is necessary to set upthe switching threshold of IC1.With the inter-face connected to a running PC,receivingdiode D7 should first be disconnected fromthe circuit or covered up so that no IR lightcan reach it.Adjust P1 until the output of IC1goes low now back-up the preset until justbefore the output of IC1 flips high and thiswill be the optimum setting of P1.Assembling the bitsTo ensure a good optical coupling betweenthe transducers in the meter and D7 and D8in the interface probe it is necessary for themto be in close physical contact.Commercialprobes are usually fitted with a magnetic col-lar that attaches to the circular steel washeron the front of the meter.The meter trans-ducers are mounted within the central area ofthis washer(see Figure 2).For our purposes itis simpler to mount D7 and D8 on a smallstrip of perforated board or plate and fix thisto the front of the meter with tape.For theprobe itself you will need a suitable piece ofperforated strip or plate and using a drill,make two 5 mm holes at a spacing of 6.5 mmabout the centre line.Diode D7 is fitted in theleft hole and D8 in the right hole.Thishome-made probe can now be fitted over thereading zone on the meter and fixed withtape or better still Velcro to allow simplerre-attachment.these features are of course pro-tected by several layers of stringentsecurity checks/passwords and arenot available to the consumer.The meter also stores power con-sumed and the average power con-sumption or load profile can be out-put periodically by using a commer-cial meter reading hand terminal.These devices are expensive and itwould not be possi