lorym

原帖由 Leopard 於 2009-9-10 02:04 PM 發表
其實你唔驚死的話可以用錶串聯拖板的live入你件電器度A
然後再用個A數乘電壓
前題係確定你件電器唔過2200W, 然後就係你相信個錶真係MAX頂到AC10A
呢D咁高手的行為, 我就唔敢做嘞

咁都唔一定係 WATT 架喎！

Motti_sir

新手學野:
唔係watt 會係d 咩??
同埋如果想度watt, 又應該點做??

jwong852

原帖由 Motti_sir 於 2009-9-12 16:36 發表
新手學野:
唔係watt 會係d 咩??
同埋如果想度watt, 又應該點做??

Power (unit is Watt) in AC circuit = Voltage(in RMS value)  x Current(in RMS value) x Power Factor.

OR

Power = Average value over a period of the integration of instaneous voltage x current.

These were taught in Electronic/Electrical Engineering year 1.

If you only have Form 5 physics level, read books of Elementory Electrical Engineering or Google "Power Factor".

[ 本帖最後由 jwong852 於 2009-9-12 19:24 編輯 ]

Motti_sir

又係喎~ 唔記得左有power factor
不過又想知, watt meter 點樣考慮埋power factor 得出正確數字?
我夾o係中間
form7 phy + o岩o岩入HDelectronic year1

jwong852

原帖由 Motti_sir 於 2009-9-12 19:22 發表
又係喎~ 唔記得左有power factor
不過又想知, watt meter 點樣考慮埋power factor 得出正確數字?
我夾o係中間
form7 phy + o岩o岩入HDelectronic year1

Analog Wattmeter 係 用voltage 推針錶一個coil (stator or rotor), current 推另一個coil. Result 就係 instantenous V x I.   針錶有隋性, 會顯示average value = true power.

Digital wattmeter 係用高速sampling, A/D. instantaneous V value X I value. (V X I 可以係正或負數) mathermatical average 就係 true power.

Vrms 同 Irms 用同樣方法, take instantaneous V value (或 I value), take square, take average, 最後要 take square root 得出 Vrms 或  Irms.

Power Factor 就要用以上result 計出黎:

P.F. = True Power / (Vrms X Irms).

我設計果個wattmeter就係咁計 :
http://www.hkepc.com/forum/viewthread.php?tid=1207998&extra=page%3D2

[ 本帖最後由 jwong852 於 2009-9-12 19:38 編輯 ]

gulakpi

Electricity is not dangerous if you know what you are doing!
The way you asked, it seemed you do not even have any knowledge of elementary physics.  Be careful, don't kill yourself!

Motti_sir

超sad~ 學校無學過true power = Prms x P.F.
最多只係計Prms 同埋P.F.
最後想問多少少野.....
true power =/= Vrms x Irms
係咪因為V同I 唔同phase?

setom

其實樓主你需要係呢類product..
http://www.hkepc.com/forum/viewthread.php?tid=1314706

等有機會再團購啦!
http://www.hkepc.com/forum/viewthread.php?tid=1317167

jackli

間唔中都會有唔少人出post...
唔理power factor