Pete Francis called me and told me the following:
a. With no drive signal to the FFB coils there is no output.
b. With no drive signal to the Hall C position modulation coils there is no input to the "lem" current monitoring box and there is a 240 Hz square wave output. Not good.
c. lem box was turned off. 240 Hz went away.
d. Dave Mack tells me the lem box is a troubleshooting tool and may be left off tonight. Current to modulation coils will pass through the lem box. PLEASE LEAVE THE LEM BOX UNPOWERED.
e. http://opsweb.acc.jlab.org/CSUEApps/atlis/task/10449 is a test plan I wrote after the 0815-0940 meeting this morning discussing the double hump in the Y positions. Note that Pete found all four coils were energized at the 240 Hz while the data shows only vertical motion. This may be a red herring.
f. I quote Pete's elog below.
http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1549334
Checking the Drive Signals for Hall C position modulation magnets today with the system enabled and off. The Drive signals had what looked to be power supply noise of 62khz 50mvdc, pulse width was 600 nanoseconds (it did not matter if Hall C position modulation was off or enabled. Checking the Hall C FFB magnet drive signals showed -50mvdc of noise on the drive signals with FFB off and FeedForward off or on did not matter.
Checking the DC output of the Hall C FFB magnets showed no dc output with no drive in. However the Hall C position modulation magnets showed a square wave output at -75mvdc at @225 hz, all 4 HAll C position modulation magnets showed this. We turned the Lem unit tied to this magnets off and the square waved on the output dc leads disappeared.
Simon and Lee were there during the test. We decided to leave the Lem unit off while Hall C takes their data tonight. I informed the PD what we had found and the status we left the lem unit in. I guess we will find out in the morning if this is the source of noise causing double peaks on the Hall C bpms.