LIQUIDARLES DE AVOLAR

This board has been designed under the framework of the AVOLAR (Alto VOLtaje para detectores de ARgón líquido) research project, which is being developed at Ciemat  (http://www.ciemat.es). Its main goal is to design a functional non-pulsating very-high-voltage source (around 1 Megavolt) devoted to liquid argon time projection chambers related to  high-energy-physics experiments.

This high voltage system is based in the Van der Graff principle, where the charge is transferred to the cathode by an liquid argon flow instead of an insulator belt.

The liquid argon is stored in several tanks which temperature and fluid level is necessary to know in order to control the experiment, refill any of the tanks, or any other operation related to the normal system functioning.

In order to monitor and control the system, a general purpose electronic board ("Liquidarles") has been developed with the aim not only to measure the fluid level, temperature and pressure, but also to measure electric field and cathode voltages, to control the middle-voltage power supply unit used to inject charges on the experiment, to monitor the system remotely, as well as to automatic manage the electro-valves circuits in charge of distributing pressurized gas along the whole system.

“Liquidarles” is an extremely flexible board whose functionality depends on the circuits implemented and on the components assembled on it.

"Liquidarles" is organized around a main controller which is a standard Arduino MEGA 2560 board who receives all the analog and digital signals and uses all this information to implement several types of Finite State Machines. It also controls the external communications.

The "Liquidarles" board has the following facilities:

1. Facilities related to the front panel
   1. LED bar array driver.
   2. Hexadecimal display with up to 8 digits.
   3. Scanning of up to 8 on-off switches.
   4. Driving up to 8 individual LEDs.
2. Facilities to measure parameters.
   1. 1 channel to measure capacitance by mean of an internal oscillator.
   2. 8 channels to offset and scale voltage signals.
   3. 4 constant current channels to drive PT100 resistors.
3. Communication facilities.
   1. In-Out port to drive external dispositive, 4 x analog / 8 x digital channels
   2. 2x3 channels to exchange analog information between up to 4 “Liquidarles” boards.
   3. XXX communication bus.
4. Power supply

"Liquidarles" board measures temperature by using standard PT100 resistors, and detects liquid gas level by determining the capacitance of a cheap sensor, made with two concentric copper pipe pieces, used as capacitor.

All analog channels are based on operational amplifiers chains which can be adapted to a particular use by setting the amplifier interconnections and the value of the resistors used.

Moreover, while the majority of the I/O Arduino ports are dedicated to only one purpose, several of them are multiplexed between different functionalities, using 0 Ohm resistors along their copper paths to select the signal destination.

ADDITIONAL NOTES

This board has been designed using KiCAD, the free and open EDA suite software (http://kicad-pcb.org/). We want to thank to the developers and the community behing this tool the great effort for improving and supporting it.

MAIN LIST OF FUNCTIONALITES:

Measurements and main control

•   Cryogenic liquid level sensor (1 channel).
•   Temperature sensors read-out (4 channels).
•   Pressure sensors read-out (4 channels).
•   Electro-valves control (up to 8 valves).

User interface

• Front panel display managing: isolated leds, led-bar, and 7 segments display array (up to 8 digits).
• On board user-selectable switches for default parameters configuration.
• Operational user control by mean of front panel switches.

Communications

• I2C communication between boards (digital backplane bus and piggy boards).
• Additional UART TX/RX communication between boards (digital backplane bus and piggy boards).
• Error signal and analog signals (up to 2) transfering between boards (analog backplane bus).

Others

• Functionality expansion with additional pluggable piggy-boards.