Comparing two AC Currents and using the output to drive a alarm circuit.

Replies

• 

  aarthivg

  consider two currents i1 and i2. these currents can be given as input to a micro controller, difference in current can be found based on the coding. if the difference in current exceeds a certain value, it will drive the relay and energize the close coil of circuit breaker in order to give supply to the alarm circuit.
• 

  Ramani Aswath

  Try using two current transformers and compare the outputs.
• 

  aarthivg

  the secondary of current transformers is generally 1 amps or 5 amps, then we need a booster to boost the current rating.
• 

  neo23

  can you name some devices which can compare ac currents? And yes i am using 2 ct s , plus i do not want to overburden them as they are already being used for metering and protection.
• 

  neo23

  Please give ideas on comparing the ac currents , as this is the main part confusing me.
• 

  aarthivg

  i think, u can code such a way to compare two currents in microcontroller.
• 

  Ramani Aswath

  neo23

  Please give ideas on comparing the ac currents , as this is the main part confusing me.

  If you can have shunts on the neutral side of the loads, the two loads being compared can have a common ground. In which case the two shunt voltages can be compared. It should be possible to amplify the differential signal and use for control.
• 

  neo23

  bioramani

  If you can have shunts on the neutral side of the loads, the two loads being compared can have a common ground. In which case the two shunt voltages can be compared. It should be possible to amplify the differential signal and use for control.

  Just like a differential relay works?
• 

  neo23

  But i am afraid sir as i have my limits. The CT s are loaded on the first hand and i have to watch that too. Perhaps microcontroller method could be less power consuming.
• 

  Ramani Aswath

  neo23

  But i am afraid sir as i have my limits. The CT s are loaded on the first hand and i have to watch that too. Perhaps microcontroller method could be less power consuming.

  What is the load on the CTs? You may still be able to take out a small signal to asuitable op amp or comparator circuit. This should not add anything to the existing load on the CT.
• 

  neo23

  Can the comparator work on AC or do i have to use an ADC in it?
• 

  Ramani Aswath

  neo23

  Can the comparator work on AC or do i have to use an ADC in it?

  If the two wave forms are in perfect phase it would work. It may be a better option to individually amplify the signal, rectify and compare.
• 

  aarthivg

  i do a similar project, when the ct current exceeds a certain value, this input is given to the micro controller to drive the relay.
• 

  neo23

  aarthivg

  i do a similar project, when the ct current exceeds a certain value, this input is given to the micro controller to drive the relay.

  Are you experimenting on Ac Current or dc? and what are you using for comparing?
• 

  aarthivg

  ac only.
• 

  neo23

  aarthivg

  ac only.

  But bro what exactly are you using for comparing? op amp ? Microcontroller? And are you using ADC to rectify the AC Currents?
• 

  aarthivg

  neo23

  But bro what exactly are you using for comparing? op amp ? Microcontroller? And are you using ADC to rectify the AC Currents?

  microcontroller and adc.
  what "bro" stands for?
• 

  Ramani Aswath

  Brother
• 

  Bionic

  All you need to do is to connect the two different ac source to two different loads of the same magnitude, then calculate each separately and read off the excess ac current, then you can now compare them...
• 

  aarthivg

  Bionic

  All you need to do is to connect the two different ac source to two different loads of the same magnitude, then calculate each separately and read off the excess ac current, then you can now compare them...

  but this needs manual calculations?
• 

  neo23

  bioramani

  If the two wave forms are in perfect phase it would work. It may be a better option to individually amplify the signal, rectify and compare.

  Bioramani sir , how about i use a null meter to see the difference in currents. I have seen null meter being used for to show the difference in two voltages. But i am not sure whether that would work out for 2 Currents.
• 

  aarthivg

  A null detector is a device built for maximum sensitivity to small voltages or currents. It is used in voltmeter circuits to indicate the absence of voltage between two points, thus indicating a condition of balance between an adjustable voltage source and the voltage being measured.
• 

  Ramani Aswath

  neo23

  Bioramani sir , how about i use a null meter to see the difference in currents. I have seen null meter being used for to show the difference in two voltages. But i am not sure whether that would work out for 2 Currents.

  If one terminal can be common you can do that without additional circuitry. Unless some sensitive info is involved and you cannot reveal data, we can advise better if we know the application, voltages involed, AC single /multiple phases and such details.
• 

  Bionic

  aarthivg

  but this needs manual calculations?

  yeaq that's what am saying you connect the two loads of same magnitude across the two ac read off the corresponding ac then do the calcutions that follow....
  Or maybe you try using a potentiometer or you design a kechoff's circuit for it hope this helps?
• 

  Ramani Aswath

  An update. This component may help:
  #-Link-Snipped-#