Andrew's Week 13 Report

Last week ended with our project failing to work after moving the circuit into its new enclosure.  To eliminate variables on the lack of operation I began replacing components and rewiring signal wires to ensure less noise in our system.  Despite these modifications our circuit was still not functioning correctly.  Finally I decided to look at the output of our shunt resistor which is used to measure current.  I reused the amplifier circuit I created several weeks prior to test the shunt.  Comparing the output wave of the shunt with the waveforms I collected several weeks prior I immediately noticed that our shunt was acting very differently.  The waveform was no longer sinusoidal but more of a spike which didnt change as our load increased or decreased.  I concluded that either the shunt resistor was broke (most likely not since it is a very simple component) or there was an increase in noise on the neutral line which I was measuring across.  Due to this Ashley ordered another shunt resistor and I was able to obtain a 150:5 current transformer from an electrical client: Wendling Quarries.  After testing the new shunt resistor there was still an odd waveform so I began changing the circuit so that the current transformer could be used to measure current. 
By using a current transformer I was able to measure current at the 120V end of the circuit which generally has less harmonic distortion present.  Also by using the CT we are able to produce a larger signal without having to dissipate much power like a shunt would.  Connecting the CT to the existing circuitry was relatively easy because the filter network stayed the same and only required the removal of the 100ohm resistors.  Finally I placed 2-2ohm resistors in parallel across the CT output which act as burden resistors to change the current into a voltage. 
Our requirements specify a circuit rating of 15 amps so at 15 amps with a 150:5 ct ratio the current produced is 500mA which forced across a resistance of 1ohm produces a signal of .5V which is the upper limit of the chips channel 1 so the full range is being utilized.  Because our signal is larger the gain in our waveform register is now set to 1 compared to it being 16 when the shunt was being used.  After adjusting the gain we have obtained satisfactory results.  I can now breathe easy.
Now that the hardware has been fixed after our malfunction with the Shunt we will concentrate on the five artifacts due next week. Shown below is the circuit enclosure with the new CT.