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Measurement System Isolation

Question asked by SparkPlugGuy on Jun 16, 2011
Latest reply on Jun 16, 2011 by AndyR

Hello, sorry if this is not the correct sub forum, it does not appear there is a topic for isolation.

 

First, I am pretty clueless when it comes to electronics.  I'm a Mechanical Engineer, so circuit design is not my strong point.  I can find my way around a circuit and I can read a circuit diagram better than most of my ME friends, but I still struggle with a lot of concepts.  Hopefully someone can help me solve my, seemingly simple, problem.

 

I am measuring the secondary voltage on an automobile ignition system using a 1:1000 clamp-on inductive voltage probe.  The probe works great and gives me a good signal on my scope.  The problem is that the probe lead is only 3 feet long.  In certain situations, the probe and the scope can be up to 30 feet apart.  Simply adding extra cable on the lead wire (BNC connected RG 59/U coax cable) works, but it changes the output of the probe.  The maximum voltage changes from 20,000volts to 17,000 volts when adding 15 extra feet of RG 59/U cable.  Plus, the signal begins to ring whent the transient response is fast enough.  I believe this is caused by the extra capacitance and inductance of the additional cable.  This change in the signal is what I am trying to fix.

 

My idea is to isolate the probe from the 30 feet of extension cable using an ADUM1100 iCoupler Digital Isolator.  I don't know if this will work or not.  The maximum voltage that needs to be isolated is 40v (40,000v max secondary voltage stepped down x1000).  I also need a chip that is a push in type, not a solder in type so I can use it on a breadboard.

 

That is the background and my idea for a solution.  Please let me if you can think of any solution to my problem or if you have any questions.

 

Thanks in advance.

 

 

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