Hi All,
I'm in the process of designing a custom made instrument for the lab. Unfortunately it's been a while since I've done any electronic work and I'm having some difficulty with developing the measurement electronics I need.
The instrument consists of two probes (labelled A and B) separated by a small distance (5 mm). An AC current is applied to A (~5 V, ~5 mA, 100 kHz) and some of this makes it to B (μA). The aim is to measure the impedance of the material between A and B, to do this I need to measure the current/voltage and phase difference between the input at A and output from B and export it to a PC (via a DAQ).
The current/voltage part I think I have sorted - my plan is to pass the current from B through an op amp, the output of this should be able to go right into the DAQ.
Where I run in to difficulty is working out a method of measuring the difference in phase between the two signals. I have found a suitable IC
(the AD8302 - http://www.analog.com/en/specialty-amplifiers/log-ampsdetectors/ad8302/products/product.html). However, I'd prefer not to use it for two reasons - it's pretty pricey (~$50) especially since I'll need a few of them and I'm not totally comfortable with soldering the TSSOP package.
As an alternative I was considering using a PLL chip. The HEF4046BP (http://www.datasheetcatalog.com/datasheets_pdf/H/E/F/4/HEF4046BP.shtml) is available in a DIP package for ~$2 and has an output from the phase comparator. My question is will this work, or is it a dumb idea?
Or TL-DR - How do I measure the phase difference between two, 200 kHz sine waves and output this as a voltage?
Thanks in advance for the help
I'm in the process of designing a custom made instrument for the lab. Unfortunately it's been a while since I've done any electronic work and I'm having some difficulty with developing the measurement electronics I need.
The instrument consists of two probes (labelled A and B) separated by a small distance (5 mm). An AC current is applied to A (~5 V, ~5 mA, 100 kHz) and some of this makes it to B (μA). The aim is to measure the impedance of the material between A and B, to do this I need to measure the current/voltage and phase difference between the input at A and output from B and export it to a PC (via a DAQ).
The current/voltage part I think I have sorted - my plan is to pass the current from B through an op amp, the output of this should be able to go right into the DAQ.
Where I run in to difficulty is working out a method of measuring the difference in phase between the two signals. I have found a suitable IC
(the AD8302 - http://www.analog.com/en/specialty-amplifiers/log-ampsdetectors/ad8302/products/product.html). However, I'd prefer not to use it for two reasons - it's pretty pricey (~$50) especially since I'll need a few of them and I'm not totally comfortable with soldering the TSSOP package.
As an alternative I was considering using a PLL chip. The HEF4046BP (http://www.datasheetcatalog.com/datasheets_pdf/H/E/F/4/HEF4046BP.shtml) is available in a DIP package for ~$2 and has an output from the phase comparator. My question is will this work, or is it a dumb idea?
Or TL-DR - How do I measure the phase difference between two, 200 kHz sine waves and output this as a voltage?
Thanks in advance for the help