go_bears
Member
I have a analog signal for kilowatts and I want to convert this to kilowatt/hr. i am using control logix ver 16. not sure if i should use the average per hour or use a totalizer for the hour. any help would be great. thanks
kilowatts to kilowatts/hr
- Thread starter go_bears
- Start date
dbh6
Lifetime Supporting Member
Try integrations.
Set a timer, with cyclic time about 1s, when the timer counts 1s check the value of power and add it one to another. after 3600 samples you have a value of power consumption in one houre.
If You want a shorter periode of time, You have to divide a sum of all samples in to a proportional part of a houre according to Your period of time.
I've hope You understand me.
Sorry for my english
Set a timer, with cyclic time about 1s, when the timer counts 1s check the value of power and add it one to another. after 3600 samples you have a value of power consumption in one houre.
If You want a shorter periode of time, You have to divide a sum of all samples in to a proportional part of a houre according to Your period of time.
I've hope You understand me.
Sorry for my english
Ken Roach
Lifetime Supporting Member + Moderator
Be clear with your nomenclature
Are you trying to calculate an average of power, or a value of energy ?
"Kilowatts / hour" and "kilowatt-hour" do not mean the same thing.
My guess is that you want to calculate energy, which is kilowatt-hours. That's a totalizer function.
Are you trying to calculate an average of power, or a value of energy ?
"Kilowatts / hour" and "kilowatt-hour" do not mean the same thing.
My guess is that you want to calculate energy, which is kilowatt-hours. That's a totalizer function.
Last edited:
dbh6
Lifetime Supporting Member
If you decide on averaging per hour
Make an array of 6 elements 0-5 for your data of the Kilowatts to be mapped to at different sample times
Start a timer with a base of 1000 and set the Preset to 3600000 which is for one hour.
Take a reading of the kilowatt from your analog signal once every 10mins, so by the time you reach an hour you will have collected data 6 times, because 6*10mins = 60mins = 1hr. Just remember that the data every 10mins will store to array 0...1...2... all the way to 5.
Finally when the timers .dn bit is set when the preset >= the Accumlator, just add up all the data your collected and divide by 6 and your will get your average reading of Kilowatt/HR, you can use a compute (CPT) function to do this.
Then right below it with a branch reset the timer and your process should keep repeating
Make an array of 6 elements 0-5 for your data of the Kilowatts to be mapped to at different sample times
Start a timer with a base of 1000 and set the Preset to 3600000 which is for one hour.
Take a reading of the kilowatt from your analog signal once every 10mins, so by the time you reach an hour you will have collected data 6 times, because 6*10mins = 60mins = 1hr. Just remember that the data every 10mins will store to array 0...1...2... all the way to 5.
Finally when the timers .dn bit is set when the preset >= the Accumlator, just add up all the data your collected and divide by 6 and your will get your average reading of Kilowatt/HR, you can use a compute (CPT) function to do this.
Then right below it with a branch reset the timer and your process should keep repeating
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TConnolly
Lifetime Supporting Member
Kilowatts is a measure of the rate of energy production/consumption. 1 watt is 1 joule per second.
So just for fun lets examine Kw/hr
. Kilowatts/hour is kJ*s-1*hour-1 = .278J*s-2 which becomes 278milligram*meters2/sec4. Raising time to the fourth power is just complete nonsense for what you most likely want, unless you are trying to do some kind of diabolical twisted physics to end the universe.
Kilowatt-hours is a measure of an amount of energy, which I suspect is what you may be wanting. The word hours in the energy unit kwh does not mandate that the energy use rate be measured over a 1 hour period. It means that it is the amount of energy used if energy is used at a constant rate of 1KW for one hour, or that 1 kwh = 1KJ*s-1*3600s = 3600KJ. Whether you use 3600KJ of energy in a millisecond, one second, one day, or one month, you have used one kilowatt-hour of energy.
So if energy consumption is what you want to measure and your energy use is not perfectly constant then you need to sample at short intervals to improve your accuracy.
Use the TOT instruction in a periodic task to totalize the kilowatts. Use a small period for the task, say maybe 100mS or 500mS. Make the gain 1. Make the timebase of the TOT 2, keeping in mind that the timebase does not dictate the time sampling and totalizing period, its there for the TOT instruction to use to compute the proper engineering units. If you were computing kilojoules instead of kwh you would use a time base of 0 to get the right units.
So just for fun lets examine Kw/hr
. Kilowatts/hour is kJ*s-1*hour-1 = .278J*s-2 which becomes 278milligram*meters2/sec4. Raising time to the fourth power is just complete nonsense for what you most likely want, unless you are trying to do some kind of diabolical twisted physics to end the universe.Kilowatt-hours is a measure of an amount of energy, which I suspect is what you may be wanting. The word hours in the energy unit kwh does not mandate that the energy use rate be measured over a 1 hour period. It means that it is the amount of energy used if energy is used at a constant rate of 1KW for one hour, or that 1 kwh = 1KJ*s-1*3600s = 3600KJ. Whether you use 3600KJ of energy in a millisecond, one second, one day, or one month, you have used one kilowatt-hour of energy.
So if energy consumption is what you want to measure and your energy use is not perfectly constant then you need to sample at short intervals to improve your accuracy.
Use the TOT instruction in a periodic task to totalize the kilowatts. Use a small period for the task, say maybe 100mS or 500mS. Make the gain 1. Make the timebase of the TOT 2, keeping in mind that the timebase does not dictate the time sampling and totalizing period, its there for the TOT instruction to use to compute the proper engineering units. If you were computing kilojoules instead of kwh you would use a time base of 0 to get the right units.
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TConnolly
Lifetime Supporting Member
At the risk of being pedantic, I want to make sure that my explanation is clear of how the timebase parameter in the TOT instruction is used for calculating the proper engineering units and not necessarily for determining the period of time over which a measurement is made.
Your input units is in kilowatts, or kilojoules/second. If you wanted to totalize using units of joules, then you have to multiply the kJ/s units by seconds so that seconds cancel and you are left with joules as your units. Since you want kwh, then the TOT instruction will multiply the input by hours (3600 seconds) so that your result is in units of 3600*kJ and the seconds units cancel, which is the definition of 1 kwh.
If that is hard to visualize then imagine you were totalizing flow. If your flow meter input is giving you gallons/second and you want to know how many gallons have gone by then you configure a time base of seconds. If your are flowing at 10 gallons/second and you have the TOT in a periodic 100mSec task then every 0.1 second TOT will add 1 gallon to the total.
10 gal/sec * .1sec = 1 gal
If your flow meter gave you gallons per hour and you were flowing at 36,000 gallons per hour and you made the time base hours then every 0.1 second the totalizer instruction will add 1 gallon to the total.
36,000gal/hour * 1hour/3600sec * .1sec = 1 gal
Hope that helps.
Your input units is in kilowatts, or kilojoules/second. If you wanted to totalize using units of joules, then you have to multiply the kJ/s units by seconds so that seconds cancel and you are left with joules as your units. Since you want kwh, then the TOT instruction will multiply the input by hours (3600 seconds) so that your result is in units of 3600*kJ and the seconds units cancel, which is the definition of 1 kwh.
If that is hard to visualize then imagine you were totalizing flow. If your flow meter input is giving you gallons/second and you want to know how many gallons have gone by then you configure a time base of seconds. If your are flowing at 10 gallons/second and you have the TOT in a periodic 100mSec task then every 0.1 second TOT will add 1 gallon to the total.
10 gal/
If your flow meter gave you gallons per hour and you were flowing at 36,000 gallons per hour and you made the time base hours then every 0.1 second the totalizer instruction will add 1 gallon to the total.
36,000gal/
Hope that helps.
the plant is using around 3800 kilowatts at a given time. i use this for the input of the TOT with a time base of 2. the total is is reset every hour. the total i am getting is around 3500. does that sound right. would be 3500 kilowatt-hour??
the meter is Integra 1530. i am still reading the manuel on this unit but it does have kWh on it. is this the unit that the power company uses for the bill?
the meter is Integra 1530. i am still reading the manuel on this unit but it does have kWh on it. is this the unit that the power company uses for the bill?
Tom Jenkins
Lifetime Supporting Member
Well, even a Bears fan deserves a little help.
If your plant is using power at the rate of 3800 kW on average then at the end of the hour you will have used 3800 kWh of energy.
Your power bill is probably quite complex. A home energy bill is generally just energy used, and the charge is so many $ per kWh. For a large user there are probably different rates for different times of day plus a charge for peak kW demand. There may be other charges besides.
It may be possible to just tie into a contact on the meter that counts kWh. In that case you just need to count the pulses and scale them.
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