Operation MethodsOM-MM04.01

29-10-2003

Method for measuring the External Joint Resistance

using Keithley DVMs

Olav Berrig

CERN – European Organization for Nuclear Research

Abstract: The External Joint Resistance measurement can presently only be done on the A – and C-clusters, because only those clusters are equipped with Keithley DVMs. The resistance is calculated as the ratio of the voltage over the external joint and the current going through the joint. The current must be constant in order to avoid inductive voltage.

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Contents

  1. Definition of the External Joint Resistance
  2. Objective of measurement
  3. Principle of measurement
  4. External Joint Resistance measurement – Test sequence
  5. Entering External Joint Resistance in Quench Table

6. Figures

7. Additional information

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1. Definition of the External Joint Resistance

The ‘external joint’ is the splice between the two apertures.

The jointsbetween upper and lower coils is not measured because the inductance from the coils generates too much noise for the measurement – otherwise we would like to measure these also.

Joints between cables of different windings (top and bottom poles and, for twin dipoles, poles of the two apertures) are accommodated outside the coils but the splice between inner cable and outer of the same pole must be fitted insidethe winding and must have low resistance, below 1 nat high field, which may be a critical point in a mass production.A novel idea to accommodate splices outside the coils is given in fig. 1.

Figure 1. Splice between two cables, from the inner and from the outer layer. The splice is not internal but brought outside the coil, in a low field region, to improve both the resistance value and the induced current effect. The design was made for the LBNL-INFN high field quadrupole for thelow-insertions. (Courtesy of S. Caspi, LBNL).

2. Objective of measurement

The resistance of the super conducting wire joints are measured because they play a major part in the heat dissipation in the magnets.The amount of cryogenic cooling in LHC is determined largely by the heat dissipation by the joints.

3. Principle of measurement

The joint resistance is measured as the voltage drop across the joint ( there are two voltage taps, one on each side on the joint ) divided by the current. The measurement isnormally done during a ‘full load line’ or a ‘mini load line’, but can also be done during special power cycles. The measuring equipment ( Keithleys ) will be damaged if a quench occurs, therefor we must be certain that the magnet is trained to a current level higher than the max. current of the power cycle. In the case where the external joint measurement is done during the full load line, the magnet must be fully trained.

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4. External Joint Resistance measurement– Test seq.

Both the voltage drop over the ‘external joint’ and the current are measured with Keithley DVMs without isolation amplifier ( therefore the Keithleys will be damaged in case of a quench ). The connection of the wires can be seen on fig 2. For the moment only the A and C clusters are equipped with Keithleys, but in the future all clusters will be equipped. Therefore, presently we can only do External joint measurement on the A- and C clusters.

The procedure is as following:

  1. Go to the test bench and connect the cables ( See Fig. 2 )
  2. Go to the local sun station(sunmta1 for Cluster A and sunmta19 for Cluster C)
  3. Open a xterm window (see Fig. 3)
  4. Type: J ( This will start the External Joint measurement program. See Fig.4)
  5. Click on: ( Keithley #6 and #11 will start acquisition)
  6. Go to the control room. Go to the console. Check magnet name.
  7. Start test e.g. Standard_MM_prog_C1.seq / Loadline_12000A_Joints_meas_c1.tst( See Fig. 6 and Fig. 7 )
  8. When the loadline is finished go to the local sun station.
  9. Click on: (You will now create a new file directory and store the data in a file in this directory e.g. FLL_23_01_04.dat - the whole path is: /opt/home/incaa/database/DVM_DAQ/Joints/<magnet name>/<file name> )
  10. Click on: ( This will start the calculation program. See Fig. 5)
  11. Click on: ( Select the directory and file which you just created )
  12. The program will by itself calculate the resistance. Note down the resistance.

5. Entering External Joint Resistance in Quench Table

The External Joint Resistance is entered in the quench table for storage on MATEST, e.g.

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Connection of cables on Cluster C:

Figure 2.

Connection of cables on Cluster A:

This bench will soon be converted to the same type as cluster C.

Make the connections on direct V-tap panel to get differential signals from direct V-taps and connect to Keithley DMM as per the following table:

Keithley No. / GPIB Address / Signal Name / Direct V-taps Points
1 / 16 / Filtered Output of IDCCT / From IDCCT Signal Conditioning Crate.
6 / 11 / External Joint / 11 - 12

Where the Direct V-taps Points are:

10 = EE112, 11 = EE113,12 = EE211, 13 = EE212, 15 = EE119, 16 = EE219

i.e. Keithley #6 is connected to EE211 and EE113

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Figure 3.

x-term window showing:

J New Joint measurement program

Figure 4.

Figure 5.

Calculate

Resistance

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7. Additional information:

The External joint measurement program is maintained by Eric Veyrunes AT/MTM/OP. In emergency you may also call Olav Berrig tel. 7675134, 163627 or (10)0450424673.

It is a labview program called: joints_measurement.vi and together with its libraries, it is stored under: /opt/home/incaa/Joints_measurement

The alias ‘J’ and the message «J --> New Joint measurement program» is made in the file: /opt/home/incaa/A_common/Aalias

which is called from: /opt/home/incaa/.tschrc

You may edit any of these files with the editor: emacs but be careful since they are system files that can block operation if an error is made.

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