I am applying 5A and reading the IRMS register. How to I convert this reading into Amps?
To convert the reading in LSBs into Amps you must gain calibrate. This is a simple step that can be performed quickly.
The basic procedure is:
1. Apply a known current to the current channel.
2. Read the RMS register; note down this value.
3. Determine the Amps/LSB constant: It is the ratio of Applied current to the RMS register reading.
4. Store this constant in your microcontroller and use it to convert all readings to ‘real world’ values.
We were calculating Vrms from the GUI and we found that we are getting different Vrms register values for the same input at different times. In this case how can we calculate the actual Vrms value from the GUI?
I think you are talking about the ADE7878 evaluation software (from your other questions on this forum). There is an option to read the averaged result from the VRMS calculation window - Refer to Figure 20 of UG146 user guide. If you click on the " Read xVRMS registers" button, you will get averaged results displayed on the window. This result should be fairly stable.
There was an error in my jumper connection. With the correct settings I am getting a pretty stable VRMS value.
In the data sheet for the ADE7878 (pg 30), it was specified that for a change in AIGAIN register the value of Vrms will change. It was stated that by writing C00000 in the AIGAIN register the Arms register value will decrease by 50% and for 400000 the Arms value will increase by 50%.
While I did my reading I however got the following results,
AIGAIN Vrms register value
The value for x400000 is the 50% increased value as per the data sheet but for C00000 it is not 50% less than the value for AIGAIN=0.
Is it possible to know why my data is not as per what is specified in the data sheet of ADE7878.
I had few more doubts that came up while I was doing energy calibration in the GUI software.
1. While calculating Apparent Power what register should I check for getting the register value of apparent power.
2. For checking the value of all other power (total, fundamental etc) is there any particular register that I can directly check in the GUI or should I look for this in the all register access.
I had calculated active power both using the ADE board and another source and these are my readings,
While doing calibration for Power calculation which registers do I need to change for getting values with more precision ?
Please find my responses below:
1. AIGAIN issue: As figure 35 of Rev.H datasheet illustrates, you have to sign extend the 23rd bit till the 27th bit. So, when you intend to write 0xC00000, you should actually write 0xFC00000. Try this out and let me know if the results are better.
2. Apparent Power: AVA, BVA, CVA registers denote the apparent powers.
3. Accessing power registers: Figure 13 of UG146 user guide shows the window that displays total and fundamental active and reactive energy registers along with apparent energy registers. For powers, "All registers access" window is the best choice. The accuracy is same no matter from which window you read a register. To get maximum accuracy from power results, try to wait for the readings to settle before you read it. Also, you should do phase calibration,if there is a significant phase error introduced by the current sensor. Offset calibration must be done when dealing with low current inputs. Can you provide the active power register value you read each time when you provide different current and voltage inputs?
Apparent Power is AVAH, BVAH and CVAH registers as per data sheet.
Current Apparent Power(AWATT register) Power found using Energy meter (Kyoritsu)
1.1A 410301 250Watt
2.3A 800003 510Watt
3.3A 1192888 750Watt
4.4A 1647004 1000Watt
These are the values we got when voltage was set at 230V from supply.
So I have to do offset calibration on this to get value of power approximately equal to the Kyoritsu reading.
1. AVAHR, BVAHR and CVAHR are apparent energy registers while AVA, BVA and CVA are apparent power registers.
2. AWATT is actually the active power register and not the apparent power register as you have stated.
3. Do you have any phase shift between V and I ? Based on your power readings (I assume they are active power measurements) from Kyoritsu meter, there is a small disconnect between V*I and the power values. If your reference meter is accurate, then it means that there is some phase shift between V and I.
4. However, I notice the issue that you are talking about. The AWATT register results do not scale well with current. Do you measure the current/voltage going into the input pins of the ADE7878 IC? Is it what you expect, in each case? Can you report those as well? Are you using CTs? Did you perform phase calibration? Offset calibration helps you when working with very low currents (say around Full_Scale/1000 or less).
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