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features exceeds the iec 61036 accuracy requirements for class 1 active energy measurement uni-directional and bi-directional power and energy measurement selectable rated conditions, led pulse rates and counter resolutions sames rm2102dse on-board precision calibration direct drive capability for both stepper motor and impulse counters opto-isolated output for connection to measurement equipment introduction this application note describes the sames reference design for a low cost, watt-hour energy meter based on the sames sa2102d integrated circuit. it is advisable to use this application note in conjunction with the sa2102d datasheet, which provides detailed information on the functionality of the sa2102d. the sa2102d is a single chip solution for accurate bi- directional power / energy measurement. it incorporates an on-chip oscillator, and has direct motor drive capabilities for stepper motors. a fast calibration led output is made available to the meter manufacturer to ensure convenient and fast calibration of the meter. the normal calibration model at a lower frequency provides for accurate and stable energy / power measurement. the device can be configured to measure either positive or negative energy, or to measure energy irrespective of the direction. the international standards iec 61036 (alternating current static watt-hour meters for active energy) was used as the primary specification for this design. the dynamic range of the meter is 800, and the meter not only easily meets this specification but exceeds the iec 61036 specification over this range. a basic meter design using the sa2102d is shown in figure 1. this design uses a shunt as the current sensing element, while the voltage is supplied to the device by means of a voltage divider circuit. calibration is done by means of a precision resistive network. the measured power is displayed on either a stepper-motor driven counter, or a mechanical impulse counter. an opto-isolator and led is connected to the output for visual inspection, or use with an optical pick-up or measurement equipment. meter specifications i , i , v as well as the pulse motor constants can be chosen by the meter designer. two examples are given later on in this document for illustration. the selection and positioning of the current and voltage sense resistors, as well as the selection and positioning of the resistor used for setting the bias are very important to ensure the correct operation of the sa2102d. the most important external components for the sa2102d integrated circuit are the current and voltage sense resistors, as well as the bias setting resistors. these resistors must be of the same type as specified in the parts list to ensure that the temperature effects and noise susceptibility are minimized. a signal of 14a must be applied to the voltage input of the sa2102d for the nominal rated mains voltage. please note that this input will saturate with currents bigger than approximately 17a (25a max), which translates into a 20% overdrive capability. this also ensures that the device will not saturate with a 10% variance in mains voltage. the mains voltage is divided down via a resistor network (see figure 2) to 14v. this voltage is fed to a 1m resistor (r18) to realize the 14a . ignoring jumpers j3...j10 results in the following equations: ra = r1 + r2 + rtrim rb = r18 || r14 where rtrim = r4 + r5 + r6 + r7 + r10 + r11 + r12 + r13 combining the two equations result in: (ra + rb) / 220v = rb / 14v values for resistors r14 = 24k , r18 = 1m are chosen. ma x b nom , rm s rm s rm s voltage input ivp circuit design analog input rm2102dse application note: reference meter watt-hour energy meter based on the sa2102d 1/16 spec-1015 (rev. 1) 29-10-02 preliminary
sames rm2102dse 2/16 http://www.sames.co.za preliminary figure 1: basic design of a watt-hour meter based on the sa2102d r2 4 r1 5 fast 7 r0 6 vdd 8 cnf 9 nc 10 vref 3 iip 2 iin 1 gnd 20 ivp 19 diri 18 diro 17 nc 16 mon 15 vss 14 led 13 mop 12 so 11 u3 r15 r16 r17 r18 r1 r2 r4 r5 r6 r7 r10 r11 r12 r13 j3 j4 j5 j6 j7 j8 j9 j10 vss vdd c6 vdd vss vdd r19 u4 resistive calibra tion network shunt live neutral r8 r9 r14 r3 d1 + c1 + c2 + c3 zd1 zd2 c5 c4 vdd vss d2 d3 c8 live mon mon+mop rated output impulse counter stepper mot or calibra tion led opto-islola ted led output vss rated conditions and led setup load vdd
substituting the values result in: rb = 23.437k ra = rb x (220v / 14v -1) ra = 396.34k standard resistor values of 100k are chosen for r1 and 180k for r2. the value of rtrim is chosen to cover 20% of ra. the values in the resistor ladder are used so that the resistor value halves with the next value. this results in using only two values in the e96 resistor range. resistors r15 and r16 (figure 3) define the current level into the current sense inputs of the sa2102d. the pm2102dp meter can be used with most available shunts. the explanation in this text is given for a 625 shunt with an i of 80a and 50mv at i . to ensure proper current sensing it is advisable to use a shunt that will give a voltage drop of at least 20mv at rated conditions. the resistor values are calculated for an input of 16a on the current sense inputs at rated conditions. the design equation is as follows: r15 = r16 = (i / 16a) x r / 2 i = line current r = shunt value also see the section on . t current sense input reference voltage ma x ma x rm s lsh l sh design examples he on chip reference current is derived from a 47k resistor sames rm2102dse 3/16 figure 2: voltage divider circuit and resistive calibration network http://www.sames.co.za connected between pin 3 of the device and vss. analog ground (gnd) the gnd pin of the sa2102d is connected to the live phase, which is halfway between v and v . the pm2102dp meter can be connected directly to live and neutral at terminals 3 and 4 on the meter-box. these terminals are internally connected to j1 on the pcb. the current must be connected to terminals 1 and 2 on the meter-box, which is internally connected to j2. dd ss pm2102dp meter setup external connectors preliminary r1 r2 r4 r5 r6 r7 r10 r11 r12 r13 j3 j4 j5 j6 j7 j8 j9 j10 neutral live in r14 rb r18 ra live in live out shunt r15 r16 iin iip figure 3: current sensing using a shunt opto-isolated pulse output current in current out live neutral 12345 6 1+2 3-4 counter figure 4: current and mains voltage connection diagram
4/16 sames rm2102dse http://www.sames.co.za preliminary the connections are made as is shown in figure 4. also see table 1. the optical-isolated pulse output is taken to the + and - terminals on the meter-box. a mechanical counter can also be connected to j21 on the pcb in place of the stepper motor counter that is currently connected to j20 on the pcb. please take note that the meter is referenced to live, and care must be taken when connecting test equipment to the meter. the pm2102dp meter is equipped with several solderable selectors , which will allow the user / meter manufacturer to set the meter up to their own specifications. table 2 describes the various jumper options. this table should be used in conjunction with figure 5, which will make it easier to locate the jumper in question. 1 figure 5: solderable selector positions and default setup. this default setup enables fast mode output, with the pulse stability circuitry enabled, for the measurement of bi- directional design examples selection of r1, r2 and r0 for different rated conditions df_led df_mo please note that the motor and pulse outputs are related to each other, thus changing the one will change the other. the following equations and tables state the basic pulse constants and motor constants obtainable with the pm2102dp meter. the output pulse equation is: led p/kwh = 1160p/sec x (1/df_led) x [3600 / ((vnom x imax) / 1000)] and the motor constant equation is: motor p/kwh = led p/kwh / df mo where dividing factors and are described in table 3 (r2, r1 and r0 are input pins for sa2102d). example 1 rated voltage: 220v rated current: 80a sensing element: shunt (80a, 50mv, 625 ) pulse constant: 800 imp/kwh motor constant: 100 imp/kwh calculate r15 and r16: r15 = r16 = (i / 16a) x r / 2 = 80a / 16a x 625 / 2. = 1.5625 k a standard value of 1k6 is chosen. the pulse constant is derived from the equation below: led p/kwh = 1160p/sec x (1 / df_led) x [3600/((vnom x imax)/1000)] = 1160 p/sec x (1 / df_led) x [3600 / (220 x 80) / 1000] 800 = 1160 p/sec x (1 / df_led ) x 204.54 1 / df_led = 0.0033717 df_led = 296 motor p/kwh = led p/kwh / df_mo 100 = 800 / df_mo df_mo = 8 lsh table 1: external connector descriptions name function description live current in neutral current out live neutral optical-isolated output. connect to measurement equipment 1 2 3 4 + and - notes 1 . solderable selectors are two pads that can be connected together by means of solder to act as a jumper. sa2102d j22 j11 j19 j3 c8 j4 j5 j6 j7 j8 j18 j17 j16 j15 j14 j9 j10 cnf fast mains j1 diro/diri shunt j2 sames r0 r1 r2 so vdd vdd vss vss
sames rm2102dse 5/16 http://www.sames.co.za preliminary solderable selector selection table 2: jumper options name these jumpers are used for calibration purposes. also see "calibrating the meter". closing a jumper will bypass the resistor in the resistor ladder. option description j3 to j10 closed leaving a jumper open will enable the resistor in the resistor ladder. open connecting to vss will allow only negative energy to be measured. j11 vss connecting to vdd will allow only positive energy to be measured. vdd connecting to jumper diro / diri will allow bi-directional energy measurement. (bi-directional is where both positive and negative energy is measured) diro / diri used to select the required rated conditions. see table 3 and 4 as well as figure 5 for further details on the various settings available. j14 vdd (+) vss used to select the required rated conditions. see table 3 and 4 as well as figure 5 for further details on the various settings available. j15 vdd (+) vss used to select the required rated conditions. see table 3 and 4 as well as figure 5 for further details on the various settings available. j16 vdd (+) vss j18 vss used to select between fast and normal pulse output mode on the calibration led output. when connected to vss the normal pulse output mode is selected. j17 vss connecting to vdd selects the fast output pulse mode. vdd (+) when fast mode is selected this input can be used to enable or disable the internal pulse stability circuitry for the led output pulses. connecting to vss disables this circuitry. j19 vss (-) connecting to vdd enables this circuitry. this selects the ic manufacturer?s test mode. for normal metering connect to vss. vdd (+)
6/16 sames rm2102dse http://www.sames.co.za preliminary r2 r1 r0 rated condition (v / i) led output (p/kwh) mon, mop (p/kwh) 0 0 0 220/10a 6400 100 0 0 1 220/20a 3200 100 0 1 0 220/40a 1600 100 0 1 1 220/80a 800 100 1 0 0 220/6a 6400 100 1 0 1 220/30a 3200 100 1 1 0 220/60a 1600 100 thus using table 3, it is seen that the closest value could be r0 = 1, r1 = 1 and r2 = 0 rated voltage: 220v rated current: 20a sensing element: shunt (80a, 50mv, 625 ) pulse constant: 3200 imp/kwh motor constant: 100 imp/kwh calculate r15 and r16: r15 = r16 = (i / 16a) x r / 2 = 20a / 16a x 625 / 2. = 390.625 a standard value of 390 is chosen. the pulse constant is derived from the equation below: motor p/kwh = led p/kwh / df_mo 100 = 3200 / df_mo df_mo = 32 thus using table 3, it is seen that the closest value could be r0 = 1, r1 = 0, and r2 = 0. in the above table a ?1? implies that the selector is connected to v . example 2 dd lsh led p/kwh = 1160p/sec x (1 / df_led) x [3600/((vnom x imax)/1000)] = 1160 p/sec x (1 / df_led) x[3600 / (220 x 20) / 1000] 3200 = 1160 p/sec x (1 / df_led ) x 818.18 1 / df_led = 0,003371 df_led = 296 table 3: df_led and df_mo factors for sa2102d r2 0 0 0 0 1 1 1 r1 0 0 1 1 0 0 1 r0 0 1 0 1 0 1 0 df_led 322 322 322 322 536 214 214 df_mo 64 32 16 8 64 16 8 calibrating the meter the meter is calibrated by means of a resistive ladder connected to the voltage input of the sa2102d. the 8 resistor values are available to choose the maximum calibration range, while the 8 jumpers provide 256 possible combinations for precise tuning. soldering a particular selector closed will short-circuit the corresponding resistor. this will in effect remove the resistor from the voltage divider, and thus provide a higher voltage at the input of r18, which is connected to the voltage input of the device. the ideal is to have 14v at the input of r18 (1m ) that supply a 14a current to the device. it is possible to over-drive this setting by plus or minus 20% and this will enable or disable the resistors in the resistor ladder to achieve the precise pulse and motor constants required. rm s standard meter constants for various rated conditions the following table list the most common and frequently used pulse and motor constants for different rated conditions. table 4 serves as an easy reference for meter manufacturers, and constants not listed can be calculated by using the equations provided in the previous examples. table 4: different meter constants
sames rm2102dse 15/16 http://www.sames.co.za 7/16 http://www.sames.co.za preliminary table 5: iec 61036 specifications current value 0.2ib i < imax 0.2ib i < imax 0.1ib i < 0.2ib 0.1ib i < 0.2ib 0.1ib i imax 0.05ib i < 0.1ib power factor 0.8 capacitive 0.5 inductive 0.8 capacitive 0.5 inductive 1 1 percentage error limits 1.0% 1.0% 1.5% 1.5% 1.0% 1.5% class 1 n/a 2.0% n/a 2.5% 2.0% 2.5% class 2 pcb design considerations there are numerous pcb design aspects to consider when designing a power/energy meter, but only a few crucial aspects will be discussed here. 1. the sense resistors on the current input (r15 and r16) must be located as close to the sa2102d-input pins as possible. this also holds true for the 1m resistor (r18), and the biasing resistor (r17). 2. the s upply bypass capacitors c4, c5 and c6 must be positioned as close as possible to the supply pins of the sa2102d, and connected to a solid ground plane. 3. it is advisable to keep the ground plane surrounding the device clear of noise that may influence the sensing signals. 4. make use of two different ground planes. the one plane should be used only for the analog section of the pcb, the other containing the power supply and digital signals. 5. the analog ground plane must be kept as quiet as possible, i.e. free from high frequency signals, and away from high voltages and currents. 6. for emc considerations, the two ground planes must only be connected at one point, preferably at the device ground pin. these two planes can also be connected via a ferrite bead that will help to suppress transients and high frequency interference from the digital to the analog plane. 7. the power supply routing and placement is also a very important aspect to consider. the power supply must be placed as far away from the analog side of the device as possible, so as not to interfere with the sensing functions. the routing must be done in such a way that all other jumpers and devices are serviced before the sa2102d device. this will ensure that all the noise (spikes and power demands) are put on the supply line before it gets to the device. most of the noise will then be filtered out by the supply bypass capacitors that are situated as close as possible to the device. 8. the meter is protected from high transients on the main voltage input by means of a etal xide aristor. these movs will clamp high transients with a sufficiently long rise time when measured with respect to neutral. 1. the onboard power supply consists of a simple capacitive divider configuration. where the output voltage is rectified by a diode pair, and held constant by means of a pair of tl431 shunt regulators. 2. the maximum current available from the supply is approximately 20ma. mo v power supply 3. please take note that the meter is fitted with a 470nf/250vac x3 type capacitor for 220vac mains supply. this capacitor must be changed to 1f/150vac x3 type when the mains supply voltage is changed to a 110vac network. figure 6 shows the schematic of the complete meter design. this meter is designed to meet the iec 61036 accuracy requirements for a class 1 meter. the iec specifications are summarized in table 5. design results
sames rm2102dse 8/16 http://www.sames.co.za figure 6: complete design preliminary r2 4 r1 5 fast 7 r0 6 vdd 8 cnf 9 nc 10 vref 3 iip 2 iin 1 gnd 20 ivp 19 diri 18 diro 17 nc 16 mon 15 vss 14 led 13 mop 12 so 11 u1 sa2102d r15 1 r16 1 r17 47k r18 1m r1 100k r2 180k r8 470r 220f 220f 820nf r9 470r r4 100k r14 24k r5 49k9 r3 47r/2w r6 24k9 d1 s10/275 r7 12k4 + c1 r10 6k2 + c2 r11 3k + c3 r12 1.5k r13 750r j3 j4 j5 j6 j7 j8 j9 j10 j1 mains c5 c4 vdd vss neutral j14 r2 j15 r1 j16 r0 j17 fast j18 cnf j20 impulse j21 count vss vdd c6 vdd vss live in j11 diro/diri vdd vss j19 so vdd vss j12 led r19 680r 1 2 j13 diro j2 shunt u4 opto j22 gnd neutral live d2 1n4148 d3 1n4148 c8 470nf/250v ac neg pos gnd tl1 tl2 c10 c9 tl431 tl431 220nf 220nf 10uf 10uf 2200uf note: to be calculated for each meter 1
sames rm2102dse 15/16 http://www.sames.co.za 9/16 http://www.sames.co.za preliminary figure 7: linearity over a dynamic range of 800 for pf = 1 sa2102d meter linearity: pf=1 -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1. 0 0 1. 2 5 1. 5 0 1. 7 5 2.00 0 . 0 1 0 . 10 1. 0 0 10 . 0 0 10 0 . 0 0 i(a m p ) %error the following performance curves show typical measurement results for instantaneous power using the sa2102d reference meter. the results are representative of the typical performance curves performance curves that can be obtained with test equipment equipped with a class 0.2 reference and a stable single-phase source.
sames rm2102dse 15/16 http://www.sames.co.za 10/16 http://www.sames.co.za figure 8: linearity at pf = +0.5 preliminary sa2102d meter linearity: pf=+0.5 figure 9: linearity at pf = -0.5 sa2102d meter linearity: pf=-0.5 -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1. 0 0 1. 2 5 1. 5 0 1. 7 5 2.00 0.01 0.10 1.00 10.00 100.00 i(a m p ) %error -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.01 0.10 1.00 10.00 100.00 i(amp) % error
sames rm2102dse 15/16 http://www.sames.co.za 11/16 http://www.sames.co.za preliminary figure 10: linearity at pf = +0.8 sa2102d meter linearity: pf=+0.8 -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1. 0 0 1. 2 5 1. 5 0 1. 7 5 2.00 0.01 0.10 1.00 10.00 100.00 i(a m p ) %error figure 11: linearity at pf = -0.8 sa2102d meter linearity: pf=-0.8 -2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1. 0 0 1. 2 5 1. 5 0 1. 7 5 2.00 0.01 0.10 1.00 10.00 100.00 i(amp) %error
sames rm2102dse 15/16 http://www.sames.co.za 12/16 http://www.sames.co.za preliminary evaluation board component list designator u1 d2, d3 tl1, tl2 r1 r2 r3 r4 r5 r6 r7 r8, r9 r10 r11 r12 r13 r14 r15, r16 r17 r18 r19 d1 j12 u4 c4, c5 c1, c2 c8 c6 c3 c9, c10 17 2 detail note 1 note 2 description 20 pin soic silicon diode precision shunt regulator, to-92 package 1% resistor metal oxide varistor red opto-isolator capacitor ceramic capacitor electrolytic radial capacitor polyester, x2 or x3 capacitor ceramic capacitor electrolytic radial capacitor tantalum m4 x 10mm 1% resistor 2w, 5% wire-wound 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 1% resistor 5% resistor part type SA2102DSA 1n4148 tl431 100k 180k 47r 100k 49k9 24k9 12k4 470r 6k2 3k 1k5 750r 24k to be calculated 47k 1m 680r s10/275 3mm led nec 2501 220nf 220f / 16v 470nf / 250vac 820nf / 16v 2200f / 16v 10f / 16v jumpers screws notes 1. calculate for specific shunt used and meter ratings. 2. use 1f / 150vac for 115v mains supply
15/16 http://www.sames.co.za 13/16 http://www.sames.co.za preliminary sames rm2102dse figure 12: top layer figure 13: bottom layer
sames rm2102dse 15/16 http://www.sames.co.za 14/16 http://www.sames.co.za preliminary figure 14: top overlay figure 15: bottom overlay c8 c3 c1 c9 c2 c10 d1 r3 j18 j17 j16 j15 j14 j13 r10 r11 r12 j9 d2 d3 j9 j7 r7 j6 r6 r4 r5 j5 j3 j4 j10 r13 j8 r14 j20 j21 cnf fast shunt j2 sa2102d sa2102d diro/diri mains j1 tl1 r6 r2 r1 tl2 opto impulse count r0 c5 j22 r18 u4 j19 j11 c4 c6 r19 so led r1 r2 r15 r17 r16
15/16 http://www.sames.co.za 15/16 http://www.sames.co.za preliminary sames rm2102dse notes:
sames pm9607ap sames rm2102dse 16/16 disclaimer: the information contained in this document is confidential and proprietary to south african micro-electronic systems (pty) ltd ("sames") and may not be copied or disclosed to a third party, in whole or in part, without the express written consent of sames. the information contained herein is current as of the date of publication; however, delivery of this document shall not under any circumstances create any implication that the information contained herein is correct as of any time subsequent to such date. sames does not undertake to inform any recipient of this document of any changes in the information contained herein, and sames expressly reserves the right to make changes in such information, without notification, even if such changes would render information contained herein inaccurate or incomplete. sames makes no representation or warranty that any circuit designed by reference to the information contained herein, will function without errors and as intended by the designer. any sales or technical questions may be posted to our e-mail address below: for the latest updates on datasheets, please visit our web site: (012) 333-6021 +27 12 333-6021 (012) 333-8071 +27 12 333-8071 energy@sames.co.za http://www.sames.co.za. south african micro-electronic systems (pty) ltd tel: tel: int fax: fax: int p o box 15888 lynn east 0039 republic of south africa 33 eland street koedoespoort industrial area pretoria republic of south africa http://www.sames.co.za preliminary

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