Common Cause Factor Estimator - Sensor/Final Element  
Item Sensors and final elements Technique
XSF YSF Applied?  
Separation  
Are all signal cables for the channels routed separately at all positions? 1 2
 
If the sensors/final elements have dedicated control electronics, is the electronics for each channel on separate printed-circuit boards? 2.5 1.5
 
If the sensors/final elements have dedicated control electronics, is the electronics for each channel indoors and in separate cabinets? 2.5 0.5
 
Diversity/Redundancy  
Do the devices employ different physical principles for the sensing elements, e.g., pressure and temperature, vane anemometer and Doppler transducer, etc? 7.5  
 
Do the devices employ different electrical principles/designs, e.g., digital and analogue, different manufacturer (not re-badged) or different technology? 5.5  
 
Do the channels employ enhanced redundancy with MooN architecture, where N > M + 2 ? 2 0.5
 
Do the channels employ enhanced redundancy with MooN architecture, where N = M + 2 ? 1 0.5
 
Are separate test methods and people used for each channel during commissioning? 1 1
 
Is maintenance on each channel carried out by different people at different times? 2.5  
 
Complexity/design/application/maturity/experience
Does cross-connection between channels preclude the exchange of any information other than that used for diagnostic testing or voting purposes? 0.5 0.5
 
Is the design based on techniques used in equipment that has been used successfully in the field for > 5 years? 1 1
 
Is there more than 5 years experience with the same hardware used in similar environments? 1.5 1.5
 
Are inputs and outputs protected from potential levels of over-voltage and over-current? 1.5 0.5
 
Are all devices/components conservatively rated (for example, by a factor of 2 or more)? 2  
 
Assessment/analysis and feedback of data  
Have the results of the FMEA or FTA been examined to establish sources of CCF and have predetermined sources of CCF been eliminated by design?   3
 
Were CC failures considered in design reviews with the results fed back into the design? (Documentary evidence of the design review activity is required.)   3
 
Are all field failures fully analysed with feedback into the design? (Documentary evidence of the procedure is required.) 0.5 3.5
 
Procedures/human interface  
Is there a written system of work to ensure that all component failures (or degradations) are detected, the root causes established and other similar items inspected for similar potential causes of failure? 0.5 1.5
 
Are procedures in place to ensure that: maintenance (including adjustment or calibration) of any part of the independent channels is staggered, and, in addition to the manual checks carried out following maintenance, the diagnostic tests are allowed to run satisfactorily between the completion of maintenance on one channel and the start of maintenance on another? 2 1
 
Do the documented maintenance procedures specify that all parts of redundant systems (for example, cables, etc.), intended to be independent of each other, are not to be relocated? 0.5 0.5
 
Is all maintenance of printed-circuit boards, etc. carried out off site at a qualified repair centre and have all the repaired items gone through a full pre-installation testing? 0.5 1.5
 
Does the system diagnostic tests report failures to the level of a field-replaceable module? 1 1
 
Competence/training/safety culture  
Have designers been trained (with training documentation) to understand the causes and consequences of common cause failures? 2 3
 
Have maintainers been trained (with training documentation) to understand the causes and consequences of common cause failures? 0.5 4.5
 
Environmental control  
Is personnel access limited (for example locked cabinets, inaccessible position)? 0.5 2.5
 
Is the system likely to operate always within the range of temperature, humidity, corrosion, dust, vibration, etc., over which it has been tested, without the use of external environmental control? 3 1
 
Are all signal and power cables separate at all positions? 2 1
 
Environmental testing  
Has the system been tested for immunity to all relevant environmental influences (for example EMC, temperature, vibration, shock, humidity) to an appropriate level as specified in recognised standards? 10 10
 
Results    
Sensors and final elements    
Beta