Problems with BOS and EOS Events

Introduction

The LGD does not require much user intervention unless something breaks. Most of the necessary tasks are performed automatically by DAQ scripts. Should something seem to be wrong, this page may help.

Enabling and Disabling BOS and EOS Gates

The LGD is read out on BOS and EOS events. The BOS events are pedestals, and the EOS events are laser monitoring. There is a flip-flop in the hut that enables these gates. Normally these are enabled when DAQ is initialized. If these gates are not present (i.e. the BOS and EOS events look like a normal events), the user can re-enable these gates with /home/mpsdaq/e852/daq/bin/enableLGD. Should one wish to disable these gates, use /home/mpsdaq/e852/daq/bin/disableLGD.

Problems with Monitoring Events

The monitoring events should cause every channel to fire, with a signal between 50 and about 3000 ADC counts (there are many reasons for this fluctuation). If they are not firing, something is wrong. The following should serve as a guide for disgnosing problems.

No channels fire, but the data events look fine. Something is wrong with the laser system. Make sure that the EOS and BOS gates are enabled. If they are, check to make sure that the laser is actaully firing. This can be checked by looking at the normalization PMT on a scope. The normalization PMT is pugged into crate 1, slot 13, channel 0x12, cable #948. You can set the laser to pulse automatically by running /home/mpsdaq/e852/daq/bin/pulse_laser <numPulses>. There should be a healthy signal. If not, check to make sure that the laser in enabled. Both the LED's on the back of the laser should be lit. If not, climb up on the trnasporter and re-enable the laser output. Have someone pulse the laser and listen for the discharges (a clicking noise). If you don't hear them, put the laser in " local " mode with the switch on the back. If it still doesn't pulse, it is dead, and will need to be replaced/repaired. Be sure to put the laser back in " remote " mode when you are done!
No channels fire, events are empty. Make sure that the ADC's are getting gates. During a spill, look at one of the gate cables and check. A 250ns gate should be present. If not, contact a trigger expert. If there is a gate, you may be experiencing a catostrophic LGD failure. Check to be sure the ADCs are working correctly ('ADC debugging guide'). See MSUHV Debugging Suggestions.
Some channels are missing, events are good
- Entire columns are missing. This is a high voltage system problem. See MSUHV Debugging Suggestions
- Channels are missing in a " checkerboard " pattern. This indicates a problem with the ADC's. Check the gates on the ADC's. If no problem is found, consult and LGD expert, and/or see the ADC debugging guide .

Problems with the Pedestal Events

The pedestals should all be about 15 ADC counts. If they are not there are several possible problems:

If the pedestal events look like data events, it is probably a problem with the gate. Try running /home/mpsdaq/e852/daq/bin/enableLGD to enable the gates. If this doesn't work, look at the gates and verify that they are there on BOS and EOS. If not, call a trigger expert.

If a small section of the detector has pedestals that are the wrong value in a " checkerboard " pattern, an ADC has probably gone bad. Consult the ADC debugging guide and `Configuring the LGD'.

If just a few pedestals are incorrect, it is not a major problem. The pedestals should be retrimmed at the next oportunity (see 'Configuring the LGD').

** 1/10/95 R.L.