Calvin&Hobbes  Setup for the Azz Experiment
	by Markus Mühlbauer

See also: Calvin&Hobbes: Event file Structure for the Azz Experiment

 

	Table of Contents

 
Setup

Running Calvin&Hobbes
The BORER Buffers
The ADCs amd TDCs
The Scalers
The IO register

	Setup

 
In the Azz experiment we have two principal groups of detectors: the polarimeter (P) and the cryo-target in combination with the neutron detector (TN). A single CAMAC crate controlled by our CES VCC 2118 Crate Controller is used to read out both detector groups. This crate holds the CAMAC units as shown in table 1.
 
 

The three Borer Buffers 1302 (polarimeter and basel chamber) are read out individually. When one of the memory banks gets full, the unit issues a LAM which generates an interupt in the VCC2118, the unit is read out and the data gets fed into the event stream. As the Borer Buffers run free and independent from each other and the rest of the electronics, no coincidences can be applied. At the end of a run, the remaining values are read out and stored.

The actual polarisation pattern must be fed into the parameter inputs  #1 (pol. 0), #2 (pol. 1) of the Borer Buffers. and therefore stored together with the corresponding ADC value in the buffer memory for later analysis

The LeCroy ADCs, Input Registers  and the Phillips TDCs  (see tables 2, and4 ) are read out all together after a master trigger (generated by some external coincidence logic) fed into the input #16 of the CAEN Input/Output register in slot 23.  The master trigger has to be delayed external by 60 to 100us to ensure that the ADCs have finished their conversions.

In order to keep the data volume small the TDCs are read out sparse and only the ADCs channels are read, which are above trigger threshold. To get the pedestals as well once and a while all ADC channels are read out.

The actual polarization is read from the c219 IO register (slot #23) and stored together with the ADC/TDC data in the event stream. To achieve this the polarisation pattern must be fed back into c219 IO register and the (undelayed!) master trigger must be connected with its strobe input.
 

The LeCroy Scalers 2551 are read out every time the polarization changes. The channel 17 of the scaler in slot 13 is read on every event and gives the time stamp value stored in the event header. Therefore it must be connected to a 1kHz clock. The veto signal from the c219 IO register is used to inhibit the counting while the polarization changes. Table 3 shows the map of the scalers.
 

The CAEN Input/Output register c219 is used to output some status bits (used by the master trigger circurrit) and to set and read the polarization (cf. table 4).  The polarization is changed every few seconds (selectable via slow control). The veto bit (bit #9) is set, the actual polarisation pattern (bits #10...#12) is cleared, the new polarisation is set (bits #6...#8) and the scaler values are read out. After a short time (~1/60s) when the polarization has changed the veto bit (bit #9) is cleared and the actual polarisation pattern is set (#bits #10...#12).

In order to syncronize all LAM sources with the polarization the actual polarization pattern must be connected to the parameter inputs (TTL) of the Borer Buffers and also feed back into the bits #13,#14 of the c219 input register. The scalers must be inhibited with the veto signal while the polarization changes.  The master trigger must be connected to the c219's strobe input to store the actual polarization selected at the trigger time and a delayed master trigger (60 to 100us) must be fed into the bit #16 for the LAM generation.
 

	Slow Control

 
The Azz experiment makes use of the new slow control features built into Calvin&Hobbes. This allows you to control the time between polarization changes and the prescale factor for the pedestal readout from the DAQcontrol program and gives you a feedback on some of the run parameters as the actual polarization, beam current  and the count rates from the various detectors/LAM sources. The parameters are assigned according to table 5.
 

Table 5: Description of the slow control parameter

#	Description	Range
0	time between polarization changes  the value can be changed only while the run is stopped	0.1-10us
1	prescale factor for the read out of the ADC pedestals  the value can be changed only while the run is stopped	1-1000
2	actual polarization	0, 1
3	beam current	0-3000nA
4	ADC/TDC LAM count rate	0-80Hz
5	rate seen by the timing scintillator	0-1kHz
6	rate seen by the left polarimeter detector	0-1kHz
7	rate seen by the right polarimeter detector	0-1kHz
8	readout lock count (gives network dropouts0	0-30
9	CAMAC errors	0-30

	List of Tables

Calvin&Hobbes: by Markus Mühlbauer  last edited: August 1998