Minipulse Plus Rev-D isn't changing voltage TP9

[monz]

Hi All,


I am using Minipulse Plus Rev-D for my project at uni to detect buried manhole covers. I have been following the instructions document closely to instruct and check the PI circuit. There is one small issue though:


All I am getting on TP9 is fluctuating noise http://tinypic.com/r/sc52so/8 (photo attached), and that voltage doesn't seem to change whenever metal is present.


I went through the documents twice double checking all the voltage readings as suggested in the document and everything else is fine.


Thank you all.


Useful info:
Coil inductance is 380uH
Coil is connected to the circuit through two wires (photo attached)
Output Frequency at is 1kHZ
"If you have an oscilloscope, then monitor the signal across the damping resistor using a x10 probe,
where you should see a flyback signal of about 350V." I am getting a fluctuating voltage for this, varies from 500mV to 4V.

[kt315]

give a pic of a signal in point TP3.

[Qiaozhi]

Hi All,


I am using Minipulse Plus Rev-D for my project at uni to detect buried manhole covers. I have been following the instructions document closely to instruct and check the PI circuit. There is one small issue though:


All I am getting on TP9 is fluctuating noise http://tinypic.com/r/sc52so/8 (photo attached), and that voltage doesn't seem to change whenever metal is present.

TP9 is the output of the second integrator.

I went through the documents twice double checking all the voltage readings as suggested in the document and everything else is fine.


Thank you all.


Useful info:
Coil inductance is 380uH
Coil is connected to the circuit through two wires (photo attached)
Output Frequency at is 1kHZ
"If you have an oscilloscope, then monitor the signal across the damping resistor using a x10 probe,
where you should see a flyback signal of about 350V." I am getting a fluctuating voltage for this, varies from 500mV to 4V.

So, now I'm a bit confused.
Why are you referring to the flyback signal at the coil, if you're looking at TP9? If the TX output is only varying by about 4V, then the TX oscillator, or the output stage, is not working. If it is, then perhaps you've forgotten to add the connection between the TX and RX pins on PL2 and PL4, as shown in Fig. 7.

[monz]

Hi Qiaozhi ,

Am I meant to connect TX and RX pins on PL2 and PL4?

Here is a photo of my current connections for PL2 and PL4 http://imgur.com/7LXFKmz

Thank you

[monz]

.

[monz]

give a pic of a signal in point TP3.

Hi Kt315,

I am getting a fluctuating signal on TP3 from 2.5V to 5V. As the signal is always changing it is hard to tell if placing a can or a coin is making any difference. I haven't noticed any consistent change when I placed a can near it.

Here is a link to a pic of the output: http://postimg.org/image/bw0eoyah9/

[monz]

Any suggestions guys?

Your help is much appreciated.

[silverdog]

As Qiaozhi says above, check your coil connections, it doesn't look like you have a GND connection