The CROME project is one of the projects of the RAMSES program and aims at developing high performance, cost effective, low maintenance radiation monitors for CERN. The project encompasses the design, the conception, the development and the series production of a new generation of read-out electronics for radiation protection monitors (CROME Measuring and Processing Unit, CMPU) as well as alarm units (CROME Alarm Unit, CAU) and uninterruptible power supply (CROME Uninterruptible Power Supply, CUPS).
CROME Measuring and Processing Unit (CMPU)
The CMPU is the main subsystem of CROME. The CMPU is composed in its basic configuration by:
- An ionisation chamber as the physical detector.
- A cylindrical metallic enclosure for the electronics that guarantees a protection index of IP54 (protection against dust and splashing water) and allows the electronics to be fixed to the ionisation chamber. The electronics part is composed of:
- The read-out electronics
- The control and processing system
- The interfacing electronics
CROME Alarm Unit (CAU)
The CAU provides visual and audible alerts to people when CROME monitor detects radiation above defined thresholds. Three coloured lamps and one siren are triggered according to three defined alert modes:
- System OK
- Alert (first alert threshold)
- Alarm (evacuation)
 Because of the criticality of this safety device, the reliability requirement is very high. The design has been made in order to reach a Safety Integrity Level 2 according to the IEC61508 standard. In order to reach this high functional reliability, the CAU embeds all necessary self-diagnostic tests to guarantee the availability of the alarm function:
- Auto-diagnostic of lights and sound devices.
- Permanent power tests.
- Intelligent fieldbus interface with transmission consistency diagnostic.
CROME Uninterruptible Power Supply (CUPS)
This unit provides a constant 24V DC power supply to CROME units such as the CMPU radiation detector and the CAU. In normal conditions, the DC power is generated from the 230 V AC main power network. In case of a main power failure, the DC power output is maintained through the internal battery. A permanent diagnostic of this battery ensures the availability of the backup power at any time.
CROME Junction Box (CJB)
The CJB is a SIL2 compliant smart interlocking signals router composed of inter-replaceable modules. The CJB has be designed to be modular by using separate I/O modules in order to be able to adapt to different physical and electrical signals. The base of the CJB is a 3U height Europa crate with a central backplane that permits the linking together of front and back modules through DIN41612 connectors.
From the back, eight I/O modules can be inserted. The width of each I/O module is 8TE (40.3mm). The goal of these I/O modules is to convert the signals coming from the external systems to logic signals and distribute them to and from the CPLDs through the backplane connexion. Each I/O module can interface up to 20 external I/O signals to the CPLDs, 10 for each CPLD. Each signal can be used as either an input or output signal, the configuration is made at the CPLD level. Different kinds of I/O modules are described below in the document. There is eight position available to insert I/O modules. The backplane connector is the same for each position; any type of I/O module can then be inserted at any position. A power entry panel permits to connect 230V AC and 24V DC power to the CJB and distribute it to the power modules through the backplane.
From the front, the two power supply modules as well as the processing module and the remote status module can be inserted. The two power supplies receive 230V AC and 24 DC inputs from the backplane and generate the 24V DC and 5V DC power rails that are distributed to all the other modules. The processing modules receive all the inputs and outputs and contain the two CPLDs that realize the logical processing. The remote status module gives access to the status of all I/Os remotely through an Ethernet connection.
