Bob Higgins <[email protected]> wrote: This is not my understanding. Most wattmeters that are implemented as you > describe require the wattmeter to be the entire target load. Otherwise, > there is no error-proof way to know how much power is dissipated in the > wattmeter in relation to that which is dissipated in the device. >
The resistor is in series with the load, as I said. The meter also measures RMS voltage and amperage. The resister is small so the temperature changes are very rapid and small. Years ago, this is how some industrial-use meters for high power worked. Okay, this is called a "thermal wattmeter." You can look that up. See, for example: https://www.yokogawa.com/ymi/tutorial/tm-tutorial_wt_12.htm Some of them have two resistance heaters, with different resistivity. > Typical wattmeter instruments have a similar deficiency as was ascribed as > an error by McKubre - I.E. taking the average of the voltage and the > average of the current and multiplying them to get the power at a sample > time. > All of the watt meters do that as well. As I recall, they had three methods of measuring the power, which were used at different power levels. - Jed
