The Hallprobe System in T24/1

In DESY Testbeam T24/1 currently two Hallprobes are installed in defined places at the PCMAG. They serve as scaling points for an analytic model of the PCMAG's B-field, developped some years ago by Christian Grefe. The probes are a design of CERN (contacts: Lucie Linssen, Felix Bergtsma).

Before the modification of PCMAG the probes were read out by a microcontroller board that would connect to a serial port in the slow control PC. However, the microprocessor would crash at arbitrary times and the entire system had to be rebooted. Four probes where connected at that time, two of which were just dangling next to the magnet.

Additional documentation can be found in the filing cabinet in the hut of T24/1.

Current System

As a long standing problem CERN has developped a new readout scheme for the probes based on a CANopen CAN-bus infrastructure. The system is called BsCAN and documented in several PDF documents:

A brief overview of the B-sensor hardware and software

BsCan software library manual

Softwarewise the CAN-bus processes are hidden from the user and everything is done via high-level commands.

CAN Bus Interface

Prerequisite is a supported CAN-bus interface. In our case we chose a PCIe card with two optically isolated channels by PEAK-System: http://www.peak-system.com/PCAN-PCI-Express.206.0.html. All products of peak are supported under Linux by a common pcan library. Details can be found on the manufacturer's website. The CAN bus is used like a network card under Linux, with ther curretn exception that the speed can't be set in the network mode.

Probes, BatCAN Boards and Cabling

The Hallprobes are read out by so called BatCAN boards. These handle the conversion between the OneWire® protocoll, used by the Hallprobes, and the CAN-bus. They also take care of the power supply. Power is supplied via extra conductors in the CAN bus cable (within standard). The bus cable is connected via a 10 pole connector. An adapter to the more common 9-pole SUB-D connector can be easily done with a 10 pole flat cable, where one line is left free at the SUB-D-end.

The cabling makes use of the full CANopen standard. A CAN bus cable has two conductors for the signal. They can accomodate several connectors and have to be terminated at both ends with 120 Ohm. The termination resistors in our setup are SMD-resistors placed inside the end connectors. In the following table the pin-assignment for both connector types is given, as well as the color code, which follows DIN 47100 with respect to the 10-pin connector:

SUB-D Pin Number

Function

10 pole Pin Number

Color

Remarks

1

not connected

1

-

2

CAN-Low

3

green

120 Ohm at cable end

3

CAN-GND

5

gray

connects to wire No. 2 of power cable (- pole)

4

GND

7

blue

connects to wire No. 2 of power cable (- pole)

5

CAN-SHIELD

9

screen

connect only on one end

6

not connected (CAN-GND)

2

-

7

CAN-High

4

yellow

120 Ohm at cable end

8

+U (6-12 V)

6

pink

connects to wire No. 1 of power cable (+ pole)

9

CAN-Power (6-12 V)

8

red

connects to wire No. 1 of power cable (+ pole)

-

-

10

-

wire left free in flat cable

Powering

Power for sensors and BatCAN modules is provided by means of a normal SUB-D connector which is only connected to two lines of a power supply (see table). The conductors are numbered, where 1 means the positive pole and 2 the negative one. The ground wire is connected to the shield and may be connected to the negative pole as well. If a symmetric power supply is used, connect wire 2 and the ground wire to the 0V terminal instead of the -6V one!

Software

Several pieces of software are used in the system:


CategoryTpc

TPCSlowControl/LPTPCHallprobes (last edited 2016-07-08 09:48:37 by GeorgVonBismarck)