2.5 Hz noise
2.5 Hz noise
I'm using an LND-712 tube and I'm finding that, in the absence of a radioactive source, the tube generates a pulse every 400 ms like clockwork. And the signal does seem to be coming from the tube, as opposed to some other component: the pulse has the profile and ~100 microsecond width that is characteristic of this model of tube. Any idea of what might be causing this?
Re: 2.5 Hz noise
That is a very strange problem, and one that I have not seen with the LND-712 before.
If you reduce the HV (turn VR1 CCW) does that affect the interval? I'm wondering if the tube voltage is slowly rising and then breaking down the gas inside the tube. If you have a 1 GOhm resistor handy (the part # is listed elsewhere in the forum) you can measure the HV supply and make sure it's in the acceptable range for the LND-712. (500V)
Since you are seeing an actual discharge of the geiger tube it is quite possible that your tube is faulty (leaky and partially filled with air). Do you have another one to test with?
If you reduce the HV (turn VR1 CCW) does that affect the interval? I'm wondering if the tube voltage is slowly rising and then breaking down the gas inside the tube. If you have a 1 GOhm resistor handy (the part # is listed elsewhere in the forum) you can measure the HV supply and make sure it's in the acceptable range for the LND-712. (500V)
Since you are seeing an actual discharge of the geiger tube it is quite possible that your tube is faulty (leaky and partially filled with air). Do you have another one to test with?
Jeff Keyzer
http://mightyohm.com
http://mightyohm.com