gg_calibration by stariya



                        Gating Grid Driver Calibration
                           for the TPC and FTPC*
                                            Jeff Wood
                                       Brookhaven ext. 7580

        This document outlines the procedure to calibrate the gating grid drivers for the
STAR TPC and FTPC. The calibration should only be done by a qualified expert. Also,
before attempting any calibration one should have the permission of either Blair
Stringfellow ( for the TPC or Volker Eckardt
( for the FTPC. The following describes the calibration procedure
specifically for the TPC. There are some differences between the TPC and FTPC control
GUIs. However, both the TPC and FTPC use the same gating grid drivers, and the basic
calibration procedure is the same for both.

1. Diagnosing the Problem

        The gating grid voltages are monitored by the TPC slow controls. A diagram of
all 48 sectors of the gating grid is shown on the gating grid monitor GUI. For normal
operation all sectors should be green. Three voltages VGG hi, VGG and VGG lo are
monitored for each sector of the gating grid. If any of the three deviate by 1% of the set
point value, then the sector will be yellow. For deviations greater than 2%, the sector
will be red.
        If a monitored voltage deviates from its set point then a calibration is necessary.
There are three things that could be happening:

           1. The voltages on the gating grid wires are correct (i.e. they match the set
              points), but the monitored values are incorrect. In this case the ADC needs re-
           2. The voltages on the gating grid wires are incorrect, but they are being
              correctly monitored. In this case the DAC needs calibration.
           3. The voltages on the gating grid wires are incorrect, and the monitored values
              are incorrect. In this case ADC and DAC calibrations are necessary.

In order to determine which of these three is happening, the gating grid voltages need to
be measured from the output lines on the back of the driver modules.

    This is a revision of the document originally authored by Eugene Yamamoto, LBNL on May 23, 2000.

2. Measuring Voltages

       To measure voltages from the gating grid driver modules, you will need access to
the STAR detector, a voltmeter (or oscilloscope), the HV probe box and pen and paper to
write down the voltages. Contact Blair Stringfellow for the location of the HV probe
box. The gating grid drivers are located on the 2nd floor platform on the south side of
STAR in rack 2A6. Follow these steps to measure the voltages:

           1. Make sure that the gating grid is ON.
           2. Go to the back of the rack, and locate the channel that you want to measure.
              There is a map with of the sector numbers posted on the door of the rack.
           3. Disconnect the cable coming from the module, and plug it into one of the
              sockets of the probe box.
           4. Use the voltmeter (or scope) to measure the voltages from the probe box.
              Note: All the measured voltages should be negative.

        For measuring VGG hi or VGG lo, the gate should be in normal mode. To
confirm this go to the TPC gating grid monitor GUI. Click on “Expert Controls” in the
upper right corner. In the window that appears, click on “Global Controls”. In this
window you should see the words “Gate NORMAL” in the VME Gate field.
        When measuring VGG hi and VGG lo from the probe box, the measured values
are given by:

           Measured VGG hi = VGG – VGG hi
           Measured VGG lo = – VGG + VGG lo

        For measuring VGG, the gate should be open. To do this go to “Expert Controls”.
In this window click on the button to change permission to “Write Enable” then click on
“Global Controls”. In this window click on the VME Gate “Enable” button. The status
should change from “Gate NORMAL” to “Gate OPEN”. You can now measure VGG
with the probe box. With the gate open, measuring either VGG hi or VGG lo from the
probe box will give the value of VGG.

3. Calibrating the ADC

        If any of the measured voltages vary from the monitored values in the gating grid
monitor GUI, then the gating grid driver ADC needs to be calibrated for those channels.
The file containing the ADC calibrations is called It can be found on* in the following directory:


The ADC calibration constant needs to be changed. First, you need to access the existing
calibration constant by connecting to the VME processor in the gating grid driver crate.
    For the FTPC the file is found on the machine

           1. From the control room, type*: telnet scserv 9002
           2. At the prompt type the following command:

               dbpr “GG_A_In_X_X”,4

               where the first X is either A, B or C. Use A for VGG hi, B for VGG lo and C
               for VGG. The second X is the channel number from 1 to 48. A chart relating
               channel number to sector number can be found on page 5.

           3. Look for the field labeled “EGUF”. This is the ADC calibration constant.
              The value of this field will be referred to as eguf

Now, the new calibration constant, eguf , must be calculated.

           eguf  = int[measured voltage/monitored voltage  eguf]

To calibrate the ADC type the following at the VME prompt:

           dbpf “GG_A_In_X_X.EGUF”,”eguf ”

where the two Xs are defined the same as in the dbpr command.
e.g. dbpf “GG_A_In_A_1.EGUF”,”262”

Copy the dbpf command and paste it to the bottom of the file. Next time
the VME is booted, the new calibration constant will be read from this file.

4. Calibrating the DAC

        If any voltages are still out of range after calibrating the ADC, then it is necessary
to recalibrate the DAC for these channels. This is done by typing the following
command at the VME prompt:

           seq &calibrate,“channel=X,sector=X”

The notation in this command is somewhat confusing. Here channel refers to either A, B
or C for VGG hi, VGG lo or VGG. While, sector refers to the channel number, 1 – 48.

        This command calibrates the DAC and creates a file in the calibrations/ directory
with a name of the form:


    To connect to the VME for the FTPC, telnet scserv 9033

Replace the appropriate line in with the line contained in this new file. This
contains the new calibration constant for the DAC. The line should look something like
       dbpf "GG_A_Out_A_10.EGUF","251.019302"

5. Further Problems

        After doing ADC and/or DAC calibrations, all voltages should be reading at or
near to their set points. If problems persist after doing calibrations, then contact Jeff
Wood or Blair Stringfellow. The problem may be due to a faulty driver module. If a
module needs to be replaced with a spare, then one should plan for approximately 3 hours
of access time.

Note: To quit VME prompt press: Control + ]
      A telnet prompt will appear. Then type: quit

Channel #   Sector #   Channel #   Sector #
     1      1 outer         25     13 outer
     2      2 outer         26     14 outer
     3      3 outer         27     15 outer
     4      4 outer         28     16 outer
     5      5 outer         29     17 outer
     6      6 outer         30     18 outer
     7      7 outer         31     19 outer
     8      8 outer         32     20 outer
     9      9 outer         33     21 outer
     10     10 outer        34     22 outer
     11     11 outer        35     23 outer
     12     12 outer        36     24 outer
     13     1 inner         37     13 inner
     14     2 inner         38     14 inner
     15     3 inner         39     15 inner
     16     4 inner         40     16 inner
     17     5 inner         41     17 inner
     18     6 inner         42     18 inner
     19     7 inner         43     19 inner
     20     8 inner         44     20 inner
     21     9 inner         45     21 inner
     22     10 inner        46     22 inner
     23     11 inner        47     23 inner
     24     12 inner        48     24 inner


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