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Hardware and software upgrade for the High Voltage Crate

Rafal Kulaga, AGH UST (Krakow)

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Table of contents

• What is the High Voltage Crate and for which tests it is used• Existing problems and shortcomings• Goals of the upgrade• Implementation details (hardware/software)• Propositions for the future work

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High Voltage Crate

• Part of the TP4 system used forTP4-B – test of circuits powered by the DFBMIC – in the high voltage part of the test (quench heater tests)DOC – test of locally powered circuits

• Test voltages up to 2400 V (2000 V with old HV power supplies)

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High Voltage Crate modules

8 Channel modulesSCHV

PS

PS

USB DAQ

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Simplified electrical schematic

Source: HV crate user manual

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Old DAQ module

PMD 1208 SN74LS373NLatches

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Goals of the upgradeProblem Implemented solution

No isolation between the crate and the PC Double isolation (2.5 KV): DAQ/Backplane, PC/DAQ

Crate connected to the PC using two cables: RS-232 cable (HV power supply) and USB cable (DAQ)

Connection with a single USB cable, DAQ module now controls the HV power supply

No transient protection leading to unreliable operation under certain circumstances

Transient protection devices used prevent disturbances even when the crate is misused; recovery methods implemented in firmware

No interlocking on the firmware level Interlocking on the level of the DAQ firmware mitigates the consequences of operator/application programmer’s mistakes

No application specific commands → need for complicated host software

DAQ is controlled using the set of around 40 application-specific commands

Possible problems with PMD 1208 drivers for future versions of MS Windows and LabView

USBTMC/USB488 drivers provided by National Instruments

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New DAQ module

MCU

Env. Sensor

I/OExpanders

EHQ Isolation

Signal ConditioningADC

DAQ/BackplaneIsolationUSB/DAQ

Isolation

PCB designed by Bruno Recordon

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New DAQ module

PCB designed by Bruno Recordon

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Transient protection

• Old DAQ was unreliable when exposed to noise/transients, due to the use of PMD 1208 card and latches to hold states of 28 digital outputs

• Because of the nature of the applications of the HV crate, DAQ will be exposed to transients and noise, so we need to protect against them

• With the old DAQ, transients were conducted to the PC through the USB cable → risk of PC damage

• During testing, we observed that some ICs used in the new DAQ can latch-up when not protected against transients

• New DAQ provides double isolation and transient protection, to mitigate these problems

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Transient protection

• D – TVS diode, works in avalanche mode, clamps voltage at a certain level

• C – works as an AC shunt to prevent undesirable energy from entering IC pins

Source: ProTek Devices TA1003

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DAQ firmware• Firmware written in C, using Atmel Studio IDE → same

environment was used for the development of the TP4 system• Firmware uses Atmel Software Framework libraries to simplify

use of timers, watchdog, I2C and USB controller• Divided into modules:

USBTMC/USB488 implementationReceives/sends data from/to the USB stack

Command interpreterParses commands and their parameters

Command executionActual implementation of the DAQ functions

Peripheral driversHV PS, SHT75, ADS1115, MCP23016

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PC/DAQ communication• DAQ communicates with the PC using USBTMC device class• Some features of the USB488 subclass are also implemented

(service requests)• Drivers available for MS Windows (NI VISA – Virtual

Instrument Software Architecture), GNU/Linux distributions (usbtmc kernel module and a version provided by Agilent Technologies), OS X (NI VISA)

ViStatus viOpen (ViSession sesn, ViRsrc name, ViAccessMode mode, ViUInt32 timeout, ViPSession vi);

ViStatus viWrite (ViSession vi, ViBuf buf, ViUInt32 cnt, ViPUInt32 retCnt);

ViStatus viRead (ViSession vi, ViPBuf buf, ViUInt32 cnt, ViPUInt32 retCnt);

ViStatus viClose (ViObject vi);

Using VISA devices in LabView

Excerpt of the C API for VISA

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USBTMC/USB488 device classes

• Simple query/answer protocol• More and more popular for test&measurement devices with

USB interfaces (along with USB CDC and HID)• Implementation of the USBTMC/USB488 device classes can be

used for different systems

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DAQ firmware - continued

usbtmc_receive()

usbtmc_execute_request()

interpret_command()

execute_device_specific_command()

usbtmc_send_response()

Command begins with :Command begins with *

DEV_DEP_MSG_OUT REQUEST_DEV_DEP_MSG_IN

usbtmc_write_response()

Parse command arguments

Execute the commandusbtmc_write_response()

Execute the command

execute_scpi_command()

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Command set

Around 40 commands divided into groups (SCPI-like)• :HVSOURCE

:HVSOURCE:VOLTAGE?:HVSOURCE:VOLTAGE:SETPOINT <integer, 0-2400>

• :THSENSOR:THSENSOR:TEMPERATURE?

• :CHANNEL:CHANNEL:VOLTAGE <integer, 1-80>

• :MEASUREMENT:MEASUREMENT:MODE <CONTINUOUS/SINGLE>:MEASUREMENT:RATE?:MEASUREMENT:GET

• :SYSTEM:SYSTEM:NAME <string>

• Some standard SCPI commands: *IDN?, *RST

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Proposals for future work

• Current design of the HV crate is around 8 years old, so it will need some attention in the future

• Communication between modules via parallel GPIO lines → extensions not possible, complicated backplane design

• Ineffective power supply – many redundant DC/DC converters used

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Proposals for future work

• Redesign all the modules: backplane, 8-channel modules, signal conditioner and power supply

• Use I2C or CAN bus for communication between modules → simplified PCB design

• Streamline power supply by eliminating redundant DC/DC converters

• Redesign the PCB in a way that reduces EMC-related problems

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Summary

Using new DAQ provides following benefits:• Simplified connection to the PC and simple programming interface• Reliable operation even when safety procedures are not duly followed by

an operator• Isolation between the PC and HV crate• More accurate measurements• Implementation of the USBTMC/USB488 device class can be used in other

systems (possibly TP4) → unified communication• Firmware upgrade through USB connection thanks to DFU (Device

Firmware Upgrade) bootloader Status:• Hardware tested and ready for production• Upgrade plan for the systems needs to be developed

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Acknowledgements

Thanks to: • Mateusz Bednarek and Jaromir Ludwin for important remarks

on the hardware and software design• Bruno Recordon for his great work on the PCB layout design

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Thank you for your attention!