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The 8800 converts analog input points as fast and as often as it can. The engineering units value (EUV) is only provided to the rest of the system if the point meets at least one of four conditions:
There are several steps in converting an analog input to its engineering units value. First a determination is made as to whether a conversion needs to be performed at all. If the point's raw value has changed by more then a spike limit and this was not the case last scan, the raw value is considered a spike and eleminated. A point that is off scan is not converted, but it is refreshed periodically at its refresh rate. A point with the short circuit test bit set (Bit-4 in the static database point flags word) will not be converted unless the raw value has changed by at least the raw value significant change amount. In all other cases, the program will attempt to perform an EU conversion and if needed provide that data to the system.
If the scanned raw value was invalid, the point is marked as in scan exception and the new EUV is the last successfully converted EUV and that is all the conversion for this point. All other points next are gain compensated. This means the point has its raw value compensation value added to the raw value and the result is multiplied by the points gain. Validity limit checking now takes place and can put the point in high or low validity alarm. Next the EU conversion is performed on the gain compensated value and the value is checked for mathematical validity. If it is not valid, the point is marked as in mathematical exception and no new EU value is generated.
Next the EU alarm level is computed for values which were converted. Finally, the point is checked for a significant change due to a change in alarm level , raw value, or EUV. If so, the data is sent to the system.
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