User`s guide

Tachometer Data
Tachometer data is identified in a time capture file with the following SDF_DATA_HDR attributes:
dataType 37 (tachometer data)
ydata_type LONG32
yIsComplex 0
scanData 0
Each point in the tachometer data is a 32 tachometer counter value which represents time. To interpret
the tachometer data, you need to know how many tachometer points are in the tachometer data, the
tachometer frequency, and the number of tachometer pulses per revolution.
number_of_tach_points = (total_rows
 total_cols − 1) num_of_points + last_valid_index
tach_pulses_per_rev = abscissa_deltaX
tach_frequency = abscissa_firstX
For each tachometer counter value in the tachometer data result (defined as tach_cnt[i]):
tach_time_sec[i] = tach_cnt[i] / tach_frequency
From each consecutive pair of tachometer points, you can compute and instantaneous RPM:
tach_pulse_delta_sec = tach_time_sec[i]
− tach_time_sec[i − 1]
tach_pulses_per_min = 60
 tach_pulses_per_sec
tach_rpm = tach_pulses_per_min / tach_pulses_per_rev
There may be a delay between the tachometer zero count value (when the tachometer started counting)
and the first sample in the time capture data. From the SDF_VECTOR_HDR associated with the
tachometer data result, you can locate the corresponding SDF_CHANNEL_HDR. The delay, in seconds,
is in the userDelay field.
There is only one tachometer result in a time capture.
Standard Data Format (SDF)
B-38