this is the datasheet can u now help me solving my question?Could you PLEASE stop with the text speak?
It would help if you post a link to the datasheet.
thak u sir,so is this IC WT7752B suitable to be used in the project 3-phase Energy meter??as u said this IC measures instantaneous power.but in electric meter used at home we need to design it which would measure in terms of KWH?..please guide...tl me the suitable IC(if any) that we can use which would further be interfaced with microcontroller..(in my project).That IC doesnt measure kWh. It outputs pulses at a rate proportional to instantaneous power (kW). You would have to feed those to a suitable counter to get kWh.
The pulse rate has no fixed relation to monitored power, since the IC relies on inputs from scaled voltage sources and from current-to-voltage transducers. You would need to calibrate the pulse rate in terms of known device-under-test voltages and currents. The IC has a CF output for calibration purposes.
Use the micro to measure the IC output pulse rate, to apply the necessary scaling factor to convert that rate to instantaneous kW, and to integrate the kW value to get kWh.
thank u sir for d support..The IC receives, for each of the 3 channels (phases), two analogue signals (voltages) Vi,Vv, proportional repectively to device-under-test (DUT) current Di and DUT voltage Dv. The proportionality constants ki,kv are unknown and depend on the sensors used to obtain Vi and Vv. The IC output pulse frequency f is proportional to Vi x Vv and hence power, but the proportionality constant is not specified. Hence the need to do a calibration by using a known DUT whose current and voltage can be measured by some means which doesn't involve the IC. If, for example, you have a DUT which when run from 240V draws 3A you know its power consumption = 240 x 3 = 720W = 0.72kW. If we assume you now use the IC to monitor that DUT and the IC produces an output frequency of 355Hz from the CF pin (I'm just using that arbitrary value for argument's sake), then the scaling factor SFcf would be 355/0.72 = 493Hz per kW (for the CF output).
Note that the 3 main outputs of the IC are frequency-divided (by some power of 2 which I can't remember) with respect to the CF output. If the division factor is R, then the overall scale factor to be applied to a main output would be SFcf/R Hz/kW.
So, for measuring energy consumed by a DUT you would need your micro to count how many pulses you get from a main output of the IC in one hour and multiply the count by SFcf/R to get kWh.
According to the datasheet 0.5V is the absolute maximum for the analog inputs. It is not good practice to run things normally at that level. You should allow for current spikes exceeding 5A.i have used a burden resistor of 750 ohms so that it gives 0.5V at its output.
I assume from the datasheet that the IC differential inputs of a given current channel would be applied directly from the respective CT burden resistor terminals, neither of which is directly grounded. I don't think you need to connect IAP/N,IBP/N or ICP/N to ground. The IC has an analog ground (to which bias circuitry for the opamps is presumably connected).in the CT section the i/p current of 5A is measured with respect to ground isn't it?
yes sir for the spikes u r talking about m using a tvs diode(bidirectional)5V.as it is mentioned in datasheet that "an overvoltage of ±6 V can be sustained on these differential current inputs without risk of permanent damage"..According to the datasheet 0.5V is the absolute maximum for the analog inputs. It is not good practice to run things normally at that level. You should allow for current spikes exceeding 5A.
I assume from the datasheet that the IC differential inputs of a given current channel would be applied directly from the respective CT burden resistor terminals, neither of which is directly grounded. I don't think you need to connect IAP/N,IBP/N or ICP/N to ground. The IC has an analog ground (to which bias circuitry for the opamps is presumably connected).
It's a pity the datasheet doesn't show a typical schematic using the IC.
Good idea.for the spikes u r talking about m using a tvs diode(bidirectional)5V
So R=V/I = 0.5/0.005 = 100 Ohm. Why then are you using 750 Ohm for your burden resistor?we calculate value of Burden resistor by formula V=IR
oh by mistake i wrote 750 ohm,m using 75 ohm .Good idea.
So R=V/I = 0.5/0.005 = 100 Ohm. Why then are you using 750 Ohm for your burden resistor?
ok.thankuThat looks ok.