Siemens CALOMAT 6 - User Manual

The CALOMAT 6 is a thermal conductivity gas analyzer designed for continuous gas analysis, particularly for use in safety-instrumented systems (SIS). It is available in various types, including CALOMAT 6F (7MB2511, 7MB2517) and CALOMAT 6E (7MB2521, 7MB2527). This device is a component of a safety-instrumented system, which typically comprises a sensor (the analyzer), a logic unit/control system (e.g., a PLC), and a final controlling element (e.g., a valve). The CALOMAT 6 contributes to safety functions by monitoring gas concentrations and providing an analog output that can be used by a logic solver to maintain a safe system status.

Function Description

The CALOMAT 6 operates based on the principle of different thermal conductivities of gases. It utilizes a micro-mechanically manufactured Si chip with a measuring diaphragm containing thin-film resistors. These resistors are maintained at a constant temperature. The current required to achieve this constant temperature varies depending on the thermal conductivity of the sample gas. This raw value is then electronically processed to calculate the gas concentration. To ensure measurement accuracy and stability, the sensor is housed in a thermostatically-controlled stainless steel enclosure to suppress ambient temperature influences. Additionally, the sensor is designed for indirect flow to prevent flow-related disturbances.

The primary safety function of the CALOMAT 6 is user-defined threshold monitoring. For safety applications, only the isolated analog output, set to 4-20 mA (NAMUR), is considered. A dangerous failure is defined as a deviation of the output current of ±5% full span. The device is suitable for monitoring limits in safety applications and meets the functional safety requirements of SIL 1 in accordance with IEC 61508 or IEC 61511-1. The relay output is exclusively used for diagnostics in safety-instrumented systems.

Important Technical Specifications

The CALOMAT 6 hardware provides failure data compliant with IEC 61508 / IEC 61511. The hardware assessment does not include an assessment of the software. Key safety characteristics for the CALOMAT 6, as per the SIL Declaration of Conformity, include:

• Device Type: B (complex component using microcontrollers or programmable logic).
• SIL Safety Integrity Level: 1.
• Hardware Fault Tolerance (HFT): 0.
• Safe Failure Fraction (SFF): 61%.
• Average Probability of Dangerous Failure on Demand (PFDAVG): 2.01 x 10^-3 (for a 12-month proof test interval).
• Safe Undetected Failure Rate (λsu): 237 FIT.
• Dangerous Detected Failure Rate (λdd): 506 FIT.
• Dangerous Undetected Failure Rate (λdu): 460 FIT.
• Mean Time To Repair (MTTR): 8 hours.
• Mean Time Between Failure (MTBF): 78 years.
• The best time to react to a dangerous detected failure is 1 hour.
• The analog output is 4-20 mA (NAMUR).
• Four freely-programmable measuring ranges per component, including suppressed zero.
• All measuring ranges are linear.
• The logic solver (PLC) must be configured to detect over-range (>21mA) and under-range (<3.6mA) failures of the CALOMAT 6, recognizing these as internal device failures rather than spurious trips.

These characteristics are valid under specific conditions: low demand mode operation, safety-related parameters entered and checked before operation, blocking against unauthorized changes, an average long-term temperature of 40°C, compatibility of all materials with process conditions, and an MTTR of 8 hours. The useful life of the Gas Analyzer CALOMAT 6 is estimated to be 10 years.

Usage Features

The CALOMAT 6 is primarily used for monitoring the concentration of hydrogen and noble gases. It offers an accuracy of ±5% of full span for its safety-instrumented function. The device is designed to be integrated into safety-instrumented systems where its analog output feeds into a logic solver (e.g., a PLC) that processes the measurement for safety-critical actions. The device's settings, particularly the analog output function (Function Number 70) to "Select 4..20 mA (Namur)," are crucial for its safety function. After configuration, access codes (Function Number 79) should be changed to protect against unauthorized modifications.

Maintenance Features

Regular maintenance and checking are essential to ensure the CALOMAT 6 continues to fulfill its safety function. It is recommended to check the device's functioning at regular intervals, ideally once a year. This involves testing the basic functionality as described in the instruction manual.

Proof Tests: To detect dangerous undetected faults in the CALOMAT 6 analog output, two proof tests must be performed:

Proof Test 1:

1. Bypass the safety PLC or take other appropriate action to avoid a false trip.
2. Generate or simulate an alarm condition to force the Gas Analyzer CALOMAT 6 to go to the high alarm current output and verify that the analog current reaches that value.
3. Generate or simulate an alarm condition to force the Gas Analyzer CALOMAT 6 to go to the low alarm current output and verify that the analog current reaches that value.
4. Restore the loop to full operation.
5. Remove the bypass from the safety PLC or otherwise restore normal operation.

Proof Test 2:

1. Bypass the safety PLC or take other appropriate action to avoid a false trip.
2. Perform Proof Test 1.
3. Perform a two-point calibration of the Gas Analyzer CALOMAT 6.
4. Perform a reference measurement with at least one measuring point between minimum and maximum concentration, using a calibration gas with a known concentration. The expected result must have a tolerance of not more than 5%.
5. Restore the loop to full operation.
6. Remove the bypass from the safety PLC or otherwise restore normal operation.

These proof tests are designed to detect more than 90% of possible "du" (dangerous undetected) failures in the CALOMAT 6. The testing intervals are determined by the PFDAVG of the individual safety circuit, with a recommended maximum interval of one year, and a recommended proof test interval of once per month.

In case of faults, the procedure described in the device operating manual should be followed. Defective devices should be sent to the Repair Department with details of the fault and the serial number for replacement.