Excess current in -NQL

Yes, we have try changing the card but that does not alter the current. It magnitude remain the same.
Actually I think we used a card used in other Torbet crate to be sure that the card is ok. We returned
the cards to the original places due to not to change the system components and not to influence the
results of the ongoing runs.

Later we have change the card with new one with the new coming 2.2M 1% resistors
(the previous cards ware with 5% resistors). The excess current is still there and is still the same.

So we decide the input card is not the responsible.

Sasho

From: Vincent Smith [mailto:Vincent.Smith@bristol.ac.uk]
Sent: Fri 9/18/2009 10:48 AM
To: Dave Cockerill
Cc: Ken Bell; Alexander Iskrenov Hristov; Wolfgang Funk
Subject: Excess current in -NQL

The attached spreadsheet shows the variation of current with voltage for
anode and dynode of -NQL, taken yesterday afternoon.

The columns are: anode volts, dynode volts, anode current, dynode current
(all these from the lemo sockets on the Torbet input card), then the CAEN
anode current, the CAEN dynode current, and finally the ratio of Torbet
volts to Torbet currents (expressed in Megohms.)

NB The Torbet values are 'as read' in mV.
For voltage readings: 1mV corresponds to 1V.
For current readings: 1mV corresponds to 100nA (or 10mV = 1uA).
For the calculation of effective resistance, I have subtracted the current
offsets.

Readings were taken up to 800V (anode and dynode together), then the values
as used in real life, A=800V, D=600V.

Finally, since Ken reports that the excess current appeared after the
resistors were changed on the input cards, which sounds very suspicious, I
tried using a different input card. The excess current is still there.
(Actually, I think we tried exchanging input cards at the time we first
noticed the excess current, didn't we Sasho?)

So the final column shows a small change of effective resistance of the
dynode with voltage, but this probably reflects the lower accuracy of the
readings at lower voltages. In any case, the trend is opposite to the anode.
It certainly looks like a short circuit in series with the 22M + 1.5M in the
dynode supply line to each VPT.

Vince.

PS I have put the CAEN firmware release numbers, etc on the new EE HV Wiki
page. Now we have to find what version the Barrel CAENs use...