Understanding Max Demand

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cmh
Posts: 6
Joined: Sat Oct 14, 2017 9:59 am

Understanding Max Demand

Post by cmh » Sat Oct 14, 2017 11:34 am

Could you post an explanation of the parameters "Max Demand Period" "Max Demand Interval" and the meaning of the Max_Demand data field in the meter response?

I would like to poll the meter and receive back the maximum power (W) that was drawn since the last poll (or zero). However, it looks like the meter is returning a number related to the peak W but not the peak itself. Can I do some math on the result to determine what the peak was?

Does setting an interval (or turning it off) change the behaviour of the meter? And does it matter if I poll faster or slower than the period?

As a suggestion, the API documentation for these parameters could be improved to better describe how to set/intepret and what the meter will do with the various settings.

Jameson
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Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA
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Re: Understanding Max Demand

Post by Jameson » Sat Oct 14, 2017 4:42 pm

Hello cmh,

I am only aware of us using the terminology "Max Demand", "Max Demand Period", and "Auto Reset Max Demand". I am not aware of our use of the term "Max Demand Interval" though I would assume this would be the same as "Max Demand Period".

You can change your meters Max Demand settings if you are connecting to the meter via a direct connection with either our iSerial or USB converter. Not via the EKM Push, however.
You can set a meters' Max Demand Period to either 15 min., 30 min. or 60 min.
With the Omnimeter v.3 models you can set the Max Demand read to reset at either Midnight, Noon or Off. (this is Done with the EKM Dash software, this is not a setting inside the meter itself)
With the Omnimeter v.4 models you can set the Max Demand read to auto reset to zero: Hourly, Daily, Weekly, Monthly or Off. (this is a setting inside the meter itself, the meter will reset the max demand automatically without input from the EKM Dash or EKM Push). The v.4 meter is preferred if you are interested in tracking Max Demand with the EKM Push system.

Max Demand is an average peak total watts for a 15, 30, or 60 minute demand period (Max Demand Periods are settable internally in meter). Some utilities charge penalties based on your max demand for one of these time periods. The max demand can be reset in the meter over RS-485. Maximum Demand is not the absolute peak value of watts, it is an average. For example, your meter may be reporting a max demand of 10,000 watts, this is the max demand that that meter has seen since it's max demand was reset. If the meter suddenly measured a 11,000 watt max demand, then the new Max Demand would be 11,000. If the meter only sees a temporary spike from 10,000 watts to 30,000 watts the max demand will not be 30,000 it will be 12,000 once the spike is averaged. Another example: if you are measuring 1000 watts for a while and then the watts spikes to 8000 watts for just a few seconds and then goes back to 1000 watts the Max Demand reading would be about 1200 watts. If you then see another spike to 8000 watts for about 7 minutes the Max Demand on the 15 minute period would be about 4000 to 5000 watts. The Max Demand value always increases, until it is reset to zero either manually or automatically (as described above with the v.4 meter)

To set up Max Demand:
https://help.ekmmetering.com/support/so ... mum-demand

We do not have a value in the meter itself "Max Watts since last poll", in order to find this value you would want to poll the meter as fast as practical (once per second to 3/4 of second is the fastest rate possible), then you would find the max watt value that you have received in your data set.
Does setting an interval (or turning it off) change the behaviour of the meter? And does it matter if I poll faster or slower than the period?
Sorry, I am not clear what you are asking here. Setting the Max Demand Period to any of the available values does not affect the operation of the meter in any way. You can poll as fast as once per 3/4 second or as slow as never, neither of these rates will affect the meters operation or accuracy. Does this answer your question?
As a suggestion, the API documentation for these parameters could be improved to better describe how to set/intepret and what the meter will do with the various settings.
Yes, we are always looking for ways that we can improve our documentation and our API documentation. Please let us know the specific area of the API docs that are less than crystal clear and we will try to improve them. We try not to throw too much into the API docs for fear that the docs would soon become overwhelming.

http://documents.ekmmetering.com/api-docs/?shell
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371

cmh
Posts: 6
Joined: Sat Oct 14, 2017 9:59 am

Re: Understanding Max Demand

Post by cmh » Sat Oct 14, 2017 7:42 pm

Again, thanks for this helpful information. It sounds like the max demand parameters aren't for me.

I will investigate polling quickly to determine the max watts myself.

Just to close the loop on the terminology, though, the term "max demand interval" is listed at the following link: http://documents.ekmmetering.com/api-do ... d-interval
It is in that RS-485 documentation that the terms "max demand interval" and (just above it) "max demand period" are not really very well defined. Where it says "Serial call to set the max demand period for the meter" it would be helpful to have a second sentence saying what this period is/does. Same for interval.

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