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Pt.2: By JOHN CLARKE Control your power costs with the: ENERGY METER Last month, we looked at the main features of the Energy Meter and described the circuit. This month, we present the full construction details and give the calibration procedure. B UILDING THE ENERGY METER is quite straightforward but make sure that you refer to our warning panel. This is not a project for the inexperienced! As shown in the photos, all the parts are mounted on two PC boards: (1) a main PC board coded 04107041 (138 x 116mm); and (2) a display PC board coded 04107042 (132 x 71mm) for the 66  Silicon Chip LCD module and switches. Note that the display board was designed to accept three different LCD modules – from Altronics, Dick Smith Electronics and Jaycar. The straightline 14-pin connection caters for the Altronics and DSE LCD modules, while the dual 7-way connection is for the Jaycar module. Altronics and Dick Smith Electron- ics both have kits for this project, so obtaining a kit will be easy. Note, however, that the Dick Smith Electronics kit is supplied with a different case to the one used for our prototype. They’ve also altered the PC board layouts slightly, to get everything to fit inside their case. In fact, their kit department built a fully-working prototype to confirm the design (see photo) and full instructions are supplied with the kit. Begin by checking the PC boards for the correct hole sizes. The LCD module and transformer require 3mm mounting holes, while the switches require 6.5mm holes. In addition, 2mm holes are required for the mains wire connections. siliconchip.com.au Fig.8: follow this layout to install the parts on the display PC board. The Altronics LCD module goes in the red position, the DSE module in the blue position and the Jaycar module in the green position. Check also that there are no breaks in the copper tracks or shorts between any of the tracks or pads. Note, however, that one of the tracks on the main board has no connection at one end (ie, near the 10Ω resistor, to the right of the transformer). This is correct – this track simply functions as an earth guard, so don’t join it to anything. Display board assembly Fig.8 shows the component layout on the display board. Install the wire link first, followed by trimpot VR1 and diodes D3-D5 (make sure the diodes are all oriented correctly) That done, install the 10µF capacitor, again taking care with polarity. It must be mounted with its leads bent at right angles, so that capacitor lies on its side against the board. This is necessary to provide clearance when the assembly is later secured to the case lid. If you are using the Altronics LCD module, the 6-way and 4-way rainbow cables need to be soldered into position now, since the LCD module covers the wiring points. Both cables should be about 120mm long. Similarly, you should also fit the six PC stakes adjacent to the switch positions – ie, two adjacent to S1, one each next to S2 & S3, and two adjacent to S4. Now for the LCD module. Both the Altronics and DSE modules are connected to the PC board using a single in line 14-pin header, while the Jaycar module uses the dual 7-pin header instead. Before mounting the module, fit two M3 x 9mm Nylon screws and nuts to the two corner positions opposing the header – see Fig.8. Do the nuts all the way up, then push the module down onto the PC board and secure it using two more Nylon nuts. Finally, make sure that the header is pushed flush against the PC board before soldering all the header pins. The display board can now be completed by installing the four pushbutton switches. The switch terminals are wired together and soldered to the PC stakes using This photo shows the completed display board assembly with the Altronics LCD module in place. Two flat ribbon cables are used to connect it to the main board, via header sockets. siliconchip.com.au August 2004  67 long term measurements, where the elapsed time and kWh tally must be kept in memory if there is a blackout. Most people will elect to leave the battery out, since they don’t need this facility. If you do intend to use the battery, solder the battery clip lead to the PC stakes. A hole is also provided on the PC board for the battery holder and this is secured using an M3 x 6mm screw, nut and shakeproof washer. A dab of silicone sealant can be used to ensure that the nut cannot come loose. Resistor R3 (680Ω, 0.5W) is installed on the PC board only if you intend using a rechargeable battery. Also, don’t install the battery clip if you elect not to use battery back-up, as it could short out other components. Although the battery holder provides a firm grip on the battery, it’s possible that the battery could come loose if the case is subject to rough treatment or vibration. To prevent this, two M3 x 15mm tapped Nylon spacers are installed on the PC board at either end of the battery, to prevent horizontal movement. Alternatively, these two Nylon spacers can be attached to the side of the case instead and at least one kit supplier has opted for this method. A third Nylon spacer is later fastened to the side of the case above the battery to prevent vertical movement, thus effectively trapping the battery in its holder (see photos). Note that all spacers should be at- Fig.9: the switch terminals are wired together and soldered to adjacent PC stakes on the display board using 0.7mm tinned copper wire. 0.7mm tinned copper wire as shown on Fig.9. Main board assembly Fig.10 shows how the parts are installed on the main PC board. Begin by installing the links and the resistors but don’t install the 0.01Ω 3W resistor (R1) or link R2 at this stage. You can use the colour code table (Table 1) as a guide to selecting each resistor but it’s also a good idea to check the values using a digital multimeter, as some colours can be hard to read. Next, install the diodes and bridge rectifier BR1, taking care to orient them as shown. That done, IC1 can be soldered directly to the PC board and a socket installed for microcontroller IC2. Don’t plug the IC in yet – that step comes later, after a few initial checks. The capacitors and crystals can be mounted now. Make sure that the 100µF and 1000µF 25V electrolytic capacitors are placed in the correct positions and check that all electrolytics are oriented correctly. Once they’re in, install transistor Q1 with its metal tab facing towards the battery. Similarly, install regulator REG1 as shown. The next step is to install PC stakes at all those points marked with a green asterisk (*). There are eight PC stakes in all. Follow these with the MOV and the 4-way and 6-way pin headers (the plastic guide tabs on the headers go towards the centre of the board). Resistor R2 is next on the agenda. It is made using 0.2mm enamelled copper wire. Note that you must remove the enamel insulation from the wire where it is soldered to the PC board, so that the solder flows onto the bare copper. This can be done by heating the wire with a soldering iron so that the insulation melts, before applying the solder. Resistor R1 (0.01Ω) can now be installed and soldered in place. Finally, complete the PC board by installing the 3-pin header (ie, to take link LK1 or LK2). Table 2: Capacitor Codes Value 100nF 33nF 1nF 33pF Battery back-up The back-up battery is required only if the Energy Meter is to be used for μF Code 0.1µF 0.033µF 0.001µF   – EIA Code   104   333   102    33 IEC Code 100n   33n   1n0   33p Table 1: Resistor Colour Codes o o o o o o o No. 2 1 5 1 1 1 68  Silicon Chip Value 2.2MΩ 10kΩ 1kΩ 680Ω 68Ω 10Ω 4-Band Code (1%) red red green brown brown black orange brown brown black red brown blue grey brown brown blue grey black brown brown black black brown 5-Band Code (1%) red red black yellow brown brown black black red brown brown black black brown brown blue grey black black brown blue grey black gold brown brown black black gold brown siliconchip.com.au Fig.10: here’s how to install the parts on the main PC board. Resistor R3 is installed only if a rechargeable backup battery is used. Do not install the battery clip lead if you are not using a back-up battery, as it may short other components. tached using M3 x 6mm Nylon screws (DO NOT use metal screws here). A countersunk Nylon screw is used to secure the spacer that’s attached to the side of the case. Attaching the header sockets The next step is to attach the ends of the rainbow cable leading from the display PC board to the 4-way and 6-way header sockets using the supplied metal crimp connectors. These are crimped to the stripped wire ends and secured in place with the insulation clamp using small pliers. The connectors are then slid into the pin header socket shells (but make sure you get the headers the right way around). That done, it’s a good idea to go back over the two boards and check that all parts are correctly oriented and are in the correct locations. Initial tests Now for some initial tests of the PC board assemblies. In the interests of safety, these tests are carried out using a low-voltage DC or AC power supply (eg, from a plugpack). The step-by-step procedure is as follows: siliconchip.com.au (1). Connect a 12V DC or 10-12V AC supply to the X and Y PC stakes adjacent to BR1. If you’re using a DC supply, it can be connected either way around since the bridge rectifier takes care of the polarity. (2). Measure the voltage between REG1’s tab and its output pin – you should get a reading of 5V. If the voltage is less than 4.75V or more than 5.25V, switch off the power immediately and check for incorrect component placement and orientation. (3). Assuming everything is OK, switch off, plug IC2 into its socket (make sure that it is oriented correctly) and adjust trimpot VR1 on the display board, so that the LCD module shows good contrast between the background and the displayed characters. (4). Check that the switches work by pressing the Function switch – the display should now show the cost in “$” rather than the “kWh” value (ie, at the lower righthand side of the display). (5). Hold the Function switch down until the display goes to the cost per WARNING! This circuit is directly connected to the 240VAC mains. As such, all parts may operate at mains potential and contact with any part of the circuit could prove FATAL. This includes the back-up battery and all wiring to the display PC board. To ensure safety, this circuit MUST NOT be operated unless it is fully enclosed in a plastic case. Do not connect this device to the mains with the lid of the case removed. DO NOT TOUCH any part of the circuit unless the power cord is unplugged from the mains socket. This is not a project for the inexperienced. Do not attempt to build it unless you know exactly what you are doing and are completely familiar with mains wiring practices and construction techniques. August 2004  69 Fig.11: this diagram shows how to install the mains wiring. Note that all mains wiring connections to the PC board should be directly soldered (do not use PC stakes to terminate these connections). kWh calibration mode. When it does, check that the initial 10.0c value can be increased with the Up switch and decreased with the Down switch. (6). Press the Clear switch and hold it down for five seconds. The display should go back to the kWh reading. Assuming it all works, you can disconnect the low-voltage power supply and move on to the next stage in the construction – installing power transformer T1 and the mains wiring. Transformer mounting Transformer T1 and the relay can now be mounted. The relay is secured using two M3 x 6mm screws and nuts, while the transformer is fastened using an M3 x 6mm screw, nut and star washer on one side and an M3 x 12mm screw, nut and star washer on the other. The latter mounting screw 70  Silicon Chip is also used to secure the earth solder lug, by fitting an additional star washer and lock nut – see Fig.12. After mounting the transformer, connect its 12.6V secondary leads to the X and Y PC stakes on the PC board. Similarly, connect its brown and blue primary wires to the Active and Neutral positions on either side of the MOV – see Fig.11. Mains wiring To ensure safety, be sure to use a plastic case to house the Energy Meter. There must be no metal screws going into this case. DO NOT use a metal case for this unit. All kits will be supplied with a 2-metre extension lead, so you don’t have to wire up the mains plug and socket. All you have to do is cut a 750mm-long section from each end of this lead, for the mains input and output cables. The remaining 500mm middle section is then used to complete the mains wiring after the input and output cables have been installed. Begin the mains wiring by stripping back about 150mm of the outer sheath from each cable, then feed the two cables through the entry holes in the case (output cable at top). Solder their Neutral leads directly to the PC board, as shown in Fig.11 (do not use PC stakes here). Shorten each lead as necessary before soldering it to the PC board but don’t make them too short – you don’t want any strain on the leads once everything is in the case. Once that’s done, you can mount the safety fuseholder (be sure to use a safety type suitable for 240VAC, as specified) and run the wiring to it. Note that the lead from the mains input cord goes to the end terminal of the fuseholder, siliconchip.com.au Use cable ties to bind the mains wiring as shown here, to prevent the wires from coming adrift. The fuseholder terminals are sheathed in heatshrink tubing and an insulated crimp connector is placed over the unused relay terminal to provide an extra margin of safety. Note, however, that all the circuitry operates at mains potential. while two other leads connect the middle terminal to the PC board and one of the relay terminals. To ensure safety, the fuseholder should be sheathed in heatshrink tubing (see photo). This involves slipping a 35mm length of heatshrink tubing over the three leads before soldering them to the fuseholder terminals. That done, the heatshrink tubing is slid into position over the fuseholder body and shrunk down with a hot-air gun. All connections to the relay are made by terminating the leads in insulated spade crimp connectors. Be sure to use a ratchet-driven crimping tool for this job, to ensure a professional result. Don’t use a cheap crimp tool as supplied with automotive terminal sets – they aren’t good enough for crimping mains connections. Note also that for safety reasons, it is wise to place a spare insulated connector over the unused NC terminal of the relay – see Fig.11. Having said siliconchip.com.au that, all parts and wiring in this unit could be at 240VAC (depending on the house wiring) but there’s no harm in minimising the risk of contact. Mains earth wiring Now for the mains earth wiring – see Fig.12. First, slip a 25mm length of 6mm-diameter heatshrink tubing over the two earth leads, then twist the bared wire ends together and feed them through the hole in the solder lug. If the wires won’t fit, it’s simply a matter of slightly enlarging the hole by running an oversize drill bit through it That done, the leads should be soldered to the lug and the heatshrink tubing pushed down over the connection and shrunk down to protect the joint and provide strain relief (see photo). Finally, the solder lug can be attached to the transformer mounting Fig.12: the mounting details for the earth solder lug. Twist the two earth wires securely together and feed them through the hole in the solder lug before soldering the connection. August 2004  71 This view shows the completed prototype (with the display board unplugged). The back-up battery is optional and won’t be needed in most cases. Note the three Nylon spacers that are used to trap the battery inside its holder. screw using another nut and shakeproof washer. This arrangement not only securely anchors the solder lug but also provides earthing for the transformer case. Be sure to follow the earthing arrangement exactly, as it’s important for safety. In particular, note that the earth wires must be soldered. DO NOT rely on a crimp connection. You can now complete the wiring by running the leads between the relay coil connection terminals and the PC board. These leads are crimped to 2.8mm spade connectors at the relay end and soldered to PC stakes at the other end. It’s a good idea to cover the latter connections with 2.8mm heatshrink tubing, to prevent the wires breaking at the PC stakes. Final assembly Now that the wiring has been com72  Silicon Chip pleted, the PC board can be secured inside the box using the four supplied self-tapping screws (one at each corner). These screws go into integral mounting pillars within the box. That done, the mains cords should be clamped securely in position using the supplied cord clamp grommets. Note that these cord clamp grommets must grip the mains cords tightly – you must not be able to pull the cords out, even if you place considerable strain on them. With the cords now secured, use cable ties to lace the mains wiring together, as shown in the photos. This not only keeps the wiring looking neat and tidy but also prevents the leads from breaking since they can no longer “move about”. Next, secure the display board to the lid of the case as shown in Fig.13.This is mounted on six M3 x 12mm Nylon spacers, which in turn are secured to the lid using M3 x 6mm countersunk Nylon screws. Important: you must use Nylon screws where indicated on the diagrams and in the text, to ensure that all mains voltages remain within the case. There must be NO metal screws protruding through the Energy Meter’s case. The display board headers can now be plugged into their corresponding header pins on the main board. That done, the optional back-up battery can be installed by fitting the battery clip, then pushing the battery down into its holder, so that it sits between the two board-mounted Nylon spacers at either end. The remaining M3 x 15mm Nylon spacer should then be installed immediately above the battery (see Figs.10 & 11) and secured using an M3 x 6mm countersunk Nylon screw. Next. place a shorting link onto siliconchip.com.au M3 x 12mm Nylon Spacers The six 12mm-long M3 Nylon spacers are secured to the lid of the case using M3 x 6mm Nylon countersink-head screws. The display is then secured to these spacers using cheesehead M3 x 6mm screws. either LK1 or LK2. Select the LK1 position if you want the relay to immediately switch on when power is restored after a brownout or blackout. Alternatively, choose the LK2 position so that the relay only switches on after an 18-minute delay when power is restored. Finally, glue the warning label into place on the side of the case (near the battery) and attach the lid, making sure that no components are shorted as the lid closes. The supplied metal screws can be used to secure the lid to the case, since they do not go inside the box. A second warning label must be securely affixed to the front panel. Calibration The Energy Meter is now ready for calibration so that it will display the correct wattage, kWh and energy costs. Calibration will also allow the brownout operation to function correctly. Make sure that the lid is fitted before plugging the unit into the mains. In particular, note that ALL parts inside the case, including the battery and display board, operate at lethal voltage (ie, 240VAC) if Active and Neutral are transposed in the house wiring (eg, behind a wall socket). In that case, the entire circuit will be live and dangerous when it is plugged in, EVEN IF THE POWER SWITCH IS OFF. For this reason, you must not remove the cover or touch any part of the circuit without first unplugging the unit from the wall socket. As detailed in the accompanying panel, the various calibration modes are accessed by holding down the Function switch. Here’s the procedure for each mode: siliconchip.com.au Fig.13: this generalised diagram shows the mounting details for the LCD module and the display board. Be sure to use Nylon screws and nuts where indicated. (1). COST: for the energy cost adjustment, the display will show CENTS/ kWh on the top line and the cost (eg, 10.1 Cents) on the lower line. The correct rate can be obtained from your electricity bill but note that some electricity suppliers have different rates, depending on the amount of electricity used. This means that you will need to decide which rate applies to the ap- pliances being measured. (2). ZERO OFFSET: the OFFSET adjustment is made without a load connected. Press the Up or Down switch so that the wattage value stays at 0.00W (if a negative value is showing, the calibration value should be increased so it shows 0.00). Generally, the value should not need to be altered much from the default setting. When changing values, The bared ends of the two mains Earth leads are twisted together, fed through the hole in the soldering lug and then soldered. A piece of heatshrink tubing is then slid down and shrunk over the connection to keep the leads together and provide strain relief. Use a small drill to enlarge the hole in the solder lug to accept the twisted Earth wires if necessary. August 2004  73 Calibration Selections (1) The first calibration selection is the ENERGY COST ADJUSTMENT. The display will show “CENTS/kWh” on the top line and the cost (eg, 10.0 cents) on the lower line. The cost/kWh can then be adjusted from 0 cents to 25.5 cents in 0.1 cent steps by using the Up and Down switches to select the required value. (2) The next calibration selection is the OFFSET. This is used to zero the wattage reading to 0.00W when no load is connected. Basically, the Offset adjustment removes the effect of crosstalk between the current and voltage signals, which could otherwise cause a wattage reading to be displayed with no load connected. Setting this adjustment also prevents the kWh reading from increasing when the load is connected but there is no load current. During calibration, the word “OFFSET” is shown on the lefthand side of the display, while the current wattage value is shown to the right. Below this is the offset calibration value, which is shown between < and > brackets. The initial value is 7 but this can be adjusted from -2048 to +2048 in steps of 1 using the Up and Down switches. Each step represents an adjustment of about 0.12% in the wattage reading. (3) The POWER adjustment is next in the sequence and is used to calibrate the kWh value. The power calibration values are adjustable from -2048 to +2048 in steps of 1, with each step representing a change of 0.0244%. This gives an overall adjustment range of ±50%. (4) Next comes the PHASE SHIFT adjustment facility. This alters the phase difference between the measured voltage and measured current. With a resistive load, the phase difference between the voltage and the current should be 0 – ie, they are in phase. However, the mains voltage monitoring and the current detection circuitry used in the Energy Meter can introduce small phase changes that need to be compensated for. These phase differences can be trimmed out in 62 4.47µs steps, ranging from -138.6µs to +138.6µs. This is equivalent to 0.08° per step at 50Hz, with a 2.49° maximum leading or lagging adjustment. (5) The next pressing of the Function switch displays the Brownout SAG LEVEL. If the mains voltage falls below this preset value, then a brownout condition is flagged on the lower lefthand side of the display (ie, the display shows “SAG”). Typically, the brownout voltage can be adjusted from 290V all the way down to 0V in 57 steps of about 5.1V each. (6) The SAG LEVEL CAL is the next mode in the sequence. This calibrates the voltage reading shown for the brownout (SAG) threshold level and the hysteresis, so that the unit trips correctly at the set voltage. This adjustment is available in 180 steps using the Up and Down switches, with each step changing the voltage reading by about 5V. (7) Next comes the SAG HYSTERESIS (Brownout hysteresis) adjustment. This sets the voltage above the SAG LEVEL to which the mains must rise before the brownout indication (SAG) switches off. Again, this voltage is typically adjustable in 5.1V steps from 0-290V. This hysteresis is included to prevent the brownout detection from repeatedly cycling on and off at the trip point. (8) The final mode is the SAG HALF CYCLES. This sets the number of mains half-cycles over which the brownout voltage must stay below the SAG Level before a brownout is detected. This factor is adjustable from 1-255 half-cycles in steps of one half-cycle. The default value is 100 (equivalent to a period of 1s for 50Hz mains), which means that the mains voltage must stay below the SAG Level for 100 half-cycles before a brownout is detected. If the brownout facility is not required, the SAG LEVEL can be set to 0V (or to a very low voltage). This will effectively disable brownout detection and power will always be applied to the appliance. Once all the calibration modes have been cycled through, pressing the Function switch again returns the display to its “normal” mode – ie, so that it shows the measured values. it is important to wait for at least 11 seconds so that the wattage value will update to its current reading with the new offset value. (3). POWER ADJUSTMENT: the POWER adjustment sets the calibration of the wattage reading. This is done by con74  Silicon Chip necting a high-current resistive load such as a two-bar radiator which can draw at least 5A (ie, a radiator with a rating of 1000W, or 1kW). Alternatively, you could use a 2.4kW radiator which draws up to 10A instead. Here’s the procedure: (a). First, you need to measure the resistance of the radiator when the elements are hot. To do this, set your multimeter to measure ohms and plug the radiator into a mains socket. Allow the elements to heat up to fully red for a few minutes, then pull out the mains plug and quickly measure the resistance of the elements by connecting the multimeter probes between the active and neutral pins on the plug. Note that this resistance will begin to drop as the elements cool. Make a note of the highest reading and repeat the procedure by heating the radiator up again. (b). Now measure the resistance the meter shows when the two probes are connected together. This may be around 0.1Ω and this value should be subtracted from the radiator element reading to obtain the true radiator resistance value. (c). Carefully measure the mains voltage using suitable mains-rated multimeter probes, with the meter set to measure 250VAC. (d). Using a calculator, square the mains voltage reading (eg, 240V x 240V = 57,600) and divide the result by the true resistance of the radiator (eg, 57,600/50.0 =1152W). The result is the wattage drawn by the radiator. (e). Plug the radiator into the Energy Meter’s socket and adjust the POWER calibration value until the display shows the calculated wattage value. Pressing the Up switch will give a higher wattage reading on the display, while the Down switch will give a lower wattage reading. Be sure to wait 11 seconds after each adjustment, so that the display has time to update. The actual value may change on each wattage update but it should average out to the calculated value. The calibration should be accurate to better than 0.5%, providing the mains voltage has not altered and the multimeter is accurate. Note that the kWh calibration is also set by calibrating the wattage reading and is effectively locked to this calibration. Typically, the wattage measured each second is divided by 3600 (the number of seconds in one hour). This divided value is then added every second to the existing kWh value. Note also that to convert from watt-hours to kWh, the value is divided by 1000. In the Energy Meter, we are obtaining the wattage over a 10.986328-second period and so we do siliconchip.com.au not divide by 3600 and then by 1000. Instead we divide by 32,768 and then by 10. The result is the same. (4). PHASE SHIFT: this adjustment is not required for most purposes. This is because we have used resistive current and voltage sensing and this will not alter the phase by any significant amount. However, phase compensation will be required if a different current sensor is used that introduces a phase error. For example if a current transformer is used in place of the 0.01Ω resistor (R1) and it introduces a phase lag of 0.2°, then a phase correction of 0.2° will be needed. The phase correction is made in the amplifier 2 signal chain. This means that a phase lag in channel 1 will require that a similar phase lag be introduced into the second channel. Note that this phase lag (or delay) in channel 2 is a positive value. Alternatively, if the current transducer introduces a phase lead, then the delay in channel 2 will need to be a negative value. The conversion from phase shift in degrees to phase shift in microseconds is made using the equation: shift in degrees = 360 x phase value in seconds x 50Hz. Alternatively, phase shift in seconds = shift in degrees/(360 x 50). For example, a 0.2° phase shift is equivalent to an 11.1µs shift. In this case, we use the closest setting which is 13.4µs (the phase settings are in 4.47µs steps). (5). BROWNOUT: four parameters must be set here: SAG LEVEL, SAG LEVEL CALibration, SAG HYSTERESIS and SAG CYCLES. The SAG LEVEL and SAG HYSTERESIS should both initially be at 0V, while SAG CYCLES should be set to 100 cycles. If these are not already set to these values, select the required mode using the Function switch and adjust the value using the Up and Down switches. If brownout detection isn’t required, simply set the SAG LEVEL to 0V and skip the following procedure by pressing the Function switch until the display shows the hours, wattage and energy consumption. For brownout calibration, just follow this step-by-step procedure: (a). Select the SAG LEVEL mode, then carefully measure the mains voltage using a multimeter with mainsrated probes (and set to read 250V AC). siliconchip.com.au The Dick Smith Electronics version is built into a plastic instrument case and features slightly revised PC board layouts to suit the new layout. Note: prototype unit pictured here. (b). Set the SAG LEVEL voltage using the Up switch until the SAG indicator shows. Check that this is the correct SAG threshold by stepping down in value to check if the SAG indication goes off. Note that these changes must be done slowly since there will be a 1-second lag for SAG detection. Note also that the voltage reading will probably not be the same as the measured mains voltage. This can be corrected by accessing the SAG LEVEL CAL mode and adjusting the reading shown on the lower line to be as close as possible to the measured mains voltage. (c). Reduce the SAG LEVEL to a suitable value for brownout detection. Setting a low voltage will reduce the likelihood of a brownout indication and if set at below 50V, will completely prevent brownout detection. Conversely, setting the SAG LEVEL voltage too high will cause nuisance brownout detection. A setting between 200V and 180V should be suitable. (d). Adjust the SAG HYSTERESIS (brownout hysteresis). This sets the voltage that the mains must rise above the SAG LEVEL before the brownout indication switches off. In other words, the mains voltage must rise by the SAG Hysteresis value above the SAG Level in order to reapply power to the appliance. Generally, a setting of about 5-15V would be suitable here but make sure that when you add this hysteresis voltage to the SAG level, the result is The top warning label must be lamin­ ated and securely attached to the outside of the case. The bottom two labels go inside the case (see photos for locations) less than the normal mains voltage. If not, the brownout detection (and indication) will remain in force after the power returns to normal (and the appliance will remain off). (e). Finally, set the SAG HALF CYCLES. You should use a value greater than 50 here, to ensure that any momentary drops in the supply voltage are not detected as a brownout. A value of 100 should be suitable. This means that the brownout must last at least one second before the relay switches off to disconnect power. That’s it – ­ your new Energy Meter SC is now ready for use. August 2004  75