Offset of the pulse induction

[Carlos]

Hello everyone. No other post if reported this issue, but as not mastered the English, it is very difficult to me your search.
My experience and my problem is this: once assembled all the components of any pulse induction detector that arm. is that when I turn the switch and adjust the offset with the oscilloscope to 0 volts with reference +12. After 5 minutes of ignition and hot once this reference components drift and up +2 volts. Where is the problem and possible solutions. The quality of the components?. the mosfet IRF740, LM318 IC etc.?
I welcome your comments.


Carlos

[Tepco]

2V offset drift after warmup is excessive and most probably caused by some component failure, considering anything else is OK (proven detector design, voltage regulators OK etc). Just about any component may cause this, offset adjustment network, feedback resistor drifting in value... but most probable cause is op-amp itself. LM318 is not known for very good DC performances, offset initially can be significant, but once adjusted should maintain reasonable stability. Replace chip and try again. Another problem may be soldering flux residue, some flux types are conductive, properly clean PCB first. Also check supply voltages to the chip (what detector design it is?)

[Carlos]

Hello Tepco. The detector is modified according to the design sandbanks Polish. as you will see in the original post, incorporates a 0.1 uF capacitor on the supply voltage, a capacitor of 100 pF between pins 2 and 3 of the LM318 and incorporate the output of the LM7808 regulators and 7908, a low pass filter consisting of a another 100uF capacitor, 100 nF and a resistor of 47 ohms..

Carlos