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- To: Chip Atkinson <tesla-at-pupman-dot-com>
- Subject: Solid State Wattmeter - Test Results
- From: "David E. Sharpe" <sccr4us-at-erols-dot-com>
- Date: Thu, 13 Mar 1997 00:13:25 -0800
- Reply-To: sccr4us-at-erols-dot-com
Chip, All I ran tests tonight on the EDN Solid State Wattmeter I've been using in a 1.0KVA wattmeter. The experimental design was basically use the controller to power a 120VAC,1.56kW floor heater. Inductance is trival (shaded pole blower) and 1500W heater. The calibration instrument used to calibrate and test this meter was a Yokogawa WT2010 1ph wattmeter. This unit is NIST traceable, has a 100Khz sampling, 12bit A/D conversion and has a measurement accuracy significantly better than +/- 1%. After inital unit calibration, 3 separate power runs were conducted, using the panel mounted analog voltmeter and current meter on the controller. The SS wattmeter (SSP) circuit voltage output (1V = 100W) was measured with a Fluke 87 true RMS digital voltmeter. The input voltage, current and power was likewise monitored on the Yokogawa. All instruments had been calibrated (either factory or less than 6 months) using NIST traceable instrumentation. SSP values listed as watts (Vmeas * 100W scaling). Run 1 Controller Yokogawa V I V*I SSP V I P %Deviation (SSP to Yokogawa) 20 2.5 50 39.7 19.69 2.29 45.0 -11.78 30 3.0 90 87.9 28.80 3.33 95.7 -8.15 40 4.1 164 151.4 37.37 4.32 162.6 -6.89 50 5.4 270 266.0 49.10 5.57 273.2 -2.63 60 6.5 390 388.5 59.10 6.64 392.3 -0.97 70 7.5 525 513.0 67.80 7.53 510.3 0.53 80 8.5 680 665.0 77.00 8.48 652.0 1.99 90 9.6 864 835.0 86.30 9.44 813.9 2.59 100 10.7 1070 1050 96.93 10.54 1022.7 2.67 110 11.7 1287 1267 106.6 11.50 1230.0 3.00 113 12.2 1379 1387 111.0 12.00 1335.0 3.89 Run 2 Controller Yokogawa V I V*I SSP V I P %Deviation (SSP to Yokogawa) 20 2.5 50 39.5 19.53 2.26 44.1 -10.43 30 3.3 99 100.9 30.70 3.54 108.9 -7.35 40 4.3 172 171.0 39.85 4.55 181.0 -5.52 50 5.5 275 271.0 49.80 5.64 280.4 -3.35 60 6.5 390 381.0 58.70 6.61 391.0 -2.56 70 7.5 525 507.0 67.80 7.52 510.0 -0.59 80 8.5 680 653.0 76.70 8.45 648.0 0.77 90 9.6 864 840.0 86.90 9.50 825.0 1.82 100 10.7 1070 1042 96.76 10.52 1018.0 2.36 110 11.7 1287 1264 106.6 11.54 1230.0 2.76 113 12.2 1379 1375 111.2 12.01 1339.0 2.69 Run 3 Controller Yokogawa V I V*I SSP V I P %Deviation (SSP to Yokogawa) 20 2.5 50 34.5 18.45 2.14 39.5 -12.66 30 3.3 99 82.0 28.00 3.23 108.9 -9.29 40 4.4 176 174.0 40.28 4.59 181.0 -5.94 50 5.3 265 253.0 48.07 5.45 265.0 -4.53 60 6.5 390 368.0 58.02 6.54 379.0 -2.90 70 7.5 525 507.0 67.86 7.53 510.0 -0.58 80 8.5 680 650.0 76.80 8.45 649.0 0.15 90 9.5 855 815.0 85.87 9.39 806.0 1.12 100 10.7 1070 1038 96.84 10.53 1018.0 1.96 110 11.7 1287 1257 106.5 11.53 1226.0 2.52 113 12.2 1379 1370 111.2 12.01 1334.0 2.70 Discussion: -Calibration time 30 minutes, time per run approximately 15 minutes, no delay between runs -Variation in system readings due to setpoint being controlled by analog panel meter (+/- 5% accuracy)on controller. -Variation in Yokogawa from calculated due to integration times, manual data entry, and TCR (temp coeff. of resistance) effects of heater element(s). Conclusions: -Solid-state wattmeter is reasonably accurate and repeatable over upper 60% of span (40-113 VAC). -Voltage not adjusted higher due to article upper measurement limit of 1.3KVA. In actual use, upper limit was not reached until 741 op-amp "bumped" the + rail at indicated 1.408KW. -Higher accuracy maybe possible by additional coordinated trimming of '0' and 'span' (and a lot of patience! :^( ), and possible replacement of 741 op-amp with a higher performance unit. +/- 5% accuracy as originally claimed in previous postings was achieved. DAVE SHARPE, TCBOR
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