TDI MSG: Timing Precision Explained

Hello,

Since we occasionally misuse the speed data from the MSG for performance measurements (K-Power, DZR, etc.), I am interested in knowing how reliable this data is.

The MSG measures the time per engine revolution and calculates the RPM (revolutions per minute) from that.
The internal timing base for speed measurement should, in my opinion, be linked to the clock crystal of the main system controller (MSG).
Translation:
"Any deviation of its operating frequency from the target value is directly and proportionally reflected as an error in the speed data, which in turn affects the performance curve (start of power reduction) and the exhaust emissions (in systems where the amount injected is speed-dependent, such as with the EGR system)."

Therefore, the question is: Does anyone here know what tolerances are specified in the technical specifications for MSG-T oscillators?

Hi Ulf,

Quote:

Therefore, the question: Does anyone here know what tolerances are specified in the technical specifications for MSG tactical quartz crystals?

I would estimate, pessimistically, a value of less than or plus/minus 150 ppm, i.e., < 0.03‰ .

The inaccuracy regarding the coarse diagnostic values (8-bit) is much higher.

Best regards, Rainer.

Rainer K. wrote:

The inaccuracy regarding the coarse diagnostic values (8-bit) is much higher.

At least, you can interpolate the log data to get the times, for example, to obtain "exact" values of 2000 and 4000 rpm.
But one is completely at the mercy of the tolerances of the quartz crystals .