1/18/2009 1:50 PM  
Posts: 40 Rating: (1) 
Does anybody remember if someone has developed one LOGO! software with energy meter function to calculate the amount of kWh produced by one heating system ? This function should be possible (Betel, have you been working on it ? ....) with two PT100 temperature sensors, and one flow meter equipped with pulse output. Hope to hear you soon... Thanks Paolo 
1/19/2009 12:53 PM  
Joined: 1/5/2007 Last visit: 9/3/2020 Posts: 1673 Rating: (561)

Hi Solar Element,  please tell me more about your sensor and the sensorsignals (data sheed) you put into the logo,  LOGO!series 80BA5 0r 0BA6)  and at witch module typ(basic or AM2) your signal gomes into the LOGO!  and the formula to calculate about the sensor values the value in kWh Best regards Betel 
Last edited by: Betel at: 1/19/2009 1:29 PM==> Meine TAGListen: "deut." 

1/19/2009 8:11 PM  
Posts: 40 Rating: (1) 
Hi Betel, good to read you. 
1/19/2009 9:26 PM  
Posts: 40 Rating: (1) 
To calculate kWh (heat energy), we have: Flow rate [kg/s] x dT [°C] x time [h] x Specific Heat [kJ/(kg °C)] = kWh In case of water as heating fluid we have: Flow rate [kg/s] x dT [°C] x time [h] x 4,186 [kJ/(kg °C)] = kWh Now, let’s see how to obtain each data: Flow rate: we can obtain the flow rate by one flow meter equipped with pulse device (digital output: on = pulse, off = waiting). Typically we have one pulse each 10 liters (10 kg) of water. For example,if we have pulses each after 60 seconds, we have a flow rate of 10 liters/min. dT = T1 –T2 is simply obtained from two PT100 sensors, say T1 and T2 with one analog comparator block time is time (in hours) between previous and next flow meter pulse signal. To obtain total amount of kWh we shouldsum (and store the value to display it)after time t1, t2, t3, … , tn: kWh (t1) = Flow rate (t1) x dT (t1) x t1 x 4,186 + kWh (t2) = Flow rate (t2) x dT (t2) x t2 x 4,186 + kWh (t3) = Flow rate (t3) x dT (t3) x t3 x 4,186 + … + kWh (tn) = Flow rate (tn) x dT (tn) x tn x 4,186 Hope I’ve explained the way it should work. Best Regards Paolo 
1/20/2009 11:04 PM  
Joined: 1/5/2007 Last visit: 9/3/2020 Posts: 1673 Rating: (561)

Hi Paolo, many thanks for the comprehensive description. Range of values (Minimum value, peak value) for Which requirements exist onto the resolution of the result in kWh? I understood that so, that the time values "tn" can be chosen dependently on the pulse frequency of the volume flow meter (or should?). Is that correct? Or the values of the tn length are supposed to be always of the same size (and in which range of values)? For which LOGO!type (0BA5 / 0BA6) the solution is supposed to be generated)? And the PT100sensors are connect over a Module LOGO! AM2 PT100?. If not I need the translation temperature to voltage). Witch values you want to know or display additional to kWh? 
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1/21/2009 7:51 AM  
Posts: 40 Rating: (1) 
...mmm... veryvery good.... and exciting!!
Minimum flow rate = 0 (no flow meter pulse), Maximum flow rate = 20 liters/min (one flow meter pulse each 30 seconds)
T1 and T2 are supposed to be between 20°C and 90°C, the difference T1  T2 will be at 0°C minimum (heating system off), and 15°C maximum (heating system at full power).
time is between 30/3600 hours (heating system at full power) and 300/3600 hours (heating system at minimum power)
maximum value9000 kWh
The difference could be negative, but only when heating system is off and not producing energy (heat), and we have no need to calculate kWh.
not only water, also propylene glicol (antifreeze fluid) for solar heating systems. Any way let's start with water and costant Specific Heat = 4,186 [kJ/kg °K], though Specific Heat istemperature dependent.
say 0000,1 kWh
tn values have to be stored and added at tn time, which is variable time (such as flow rate). AsI wrote before, time is between 30/3600 = 0,008333hours (heating system at full power) and 300/3600 = 0,083333hours (heating system at minimum power)
OBA5
AM2 PT100 Module
Yes, instant heating system power that is the same kWh formula, but without time [h]: Flow rate [kg/s] x dT [°C] x Specific Heat [kJ/(kg °C)] = kW (power)
It's a pleasure. Thanks a lot for your time !!! Best regards Paolo 
1/29/2009 10:03 PM  
Joined: 1/5/2007 Last visit: 9/3/2020 Posts: 1673 Rating: (561)

Hi Paolo, now i can present you my final solution(s) for your posted aims. The LOGO! and special the series 0BA5 give us some difficult problems to solve: The EXCELfile "Energy_meter_calculations.xls" perhaps can help you to understand my way of solution. One result is, that the measuring/caltulation of energy kWh can done without the know of the time distancs of the sensor pulses (because the volume is constant 10 l). The suitable scaling of the values and the calculation steps are most importent to get a solution. Please look at the comments at the files. Look at "DEMO_energy_meter_kWh_V1.lsc" how to calculate and display energy kWh. Page 1 contains the inputs and there preparation. I implementedtwo versions to get/calculate the temperatur difference! At page 2 you find the part to add the smal fractions of energy evers puls and creates an internal puls to count the result sum of energy. Optional you can use pulses to external application(s). The file contains two methods to display the result... The second version "DEMO_energy_meter_V2 (with flow rate).lsc" containe an extension of file "..V1.." to mesaure/calculate the flow rate (at page 3). To measure the time between two pulses is no solution, because a division with this value is impossible. I used the way over the detection of n pulses per time window, based at my circuit "Demo_Threshold_trigger_en.lsc". The easier use of the internal block "threshold trigger" is not realy possible, because no scaling and no use of the resuls is possible then. The third version "DEMO_energy_meter_V3 (with heat power kW).lsc" containe an extension of file "..V2.." to calculate the heat power in relation of the detected flow rate. But, because there is no multiplication with a measured time (between two pulses) with LOGO! 0BA5 available, i used the n possible results of flow rate to select a calculation way ("flow rate * cp" as explicite constant values; at page 4) to display a value for the actual heat power (= at the last time window = 300 s). Now a additional comment: I have found a difference working of the version 5 and 6 of the Software LOGO!SoftComfort. Remember that the circuit part at page 2 in "DEMO_energy_meter_kWh_V1.lsc" works well in LSC version 5 and 6 and at a real LOGO!module . Look at the file "DEMO_energy_meter_kWh_V1b (LogoSoftComfort_V6).lsc", witch works well with LSC version 6  but not with LSC version 5. Sorry but i dont now what a real LOGO! is doing with that circuit version V1b. It should work well  please test this and tell me your result. If it works well too, then you can change all versions V1 to V3 of my solution files (that saves blocks). AttachmentFORUM_Energy_meter_01.zip (1457 Downloads) 
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1/30/2009 9:45 AM  
Posts: 40 Rating: (1) 
Hi Betel, many thanks for your time and professionality. As soon as possible I'll take some time to study your solution. Thanks in advance Best Regards Paolo 
7/21/2009 1:56 PM  
Posts: 40 Rating: (1) 
Hi Betel, I've implemented your software for the Energy Meter (kWh) on my last solar thermal system and I can say it works very good !! Betel, many thanks for your brilliant ideas and enthusiasm !!! Best Regards Paolo 
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