RPM Measurement
To calculate Revolutions per Minute, select RPM in the drop-down box:
Also, set the CAN ID where The K Box will transmit the result.
Set the Rate you wish to measure at:
Select the edge you wish to normalise measuring the revolutions on.
The Rate parameter affects the measurement precision.
The K-Box measures RPM using a pulse counter for the selected rate and normalises it to 1 minute to calculate the output value.
RPM = Ratenute * N pulses / Rate.
The K-Box averages the measured values if RPM changes over the measurement interval.
Example:
If the Selected Rate = 500ms.
If a Sensor sends 2000rpm for 300ms (sensor generates 2000 pulses per minute)
The KBox registers 10 pulses (10 = 2000rpm * 0.3s/60s).
If it then sends 4800 rpm for 200ms (sensor generates 4800 pulses per minute).
The KBox registers a further 16 pulses (16 = 4800rpm * 0.2s/60s)
For the whole measurement interval (500ms), the KBox registers will register a total of 26 pulses.
The Normalised value calculated will be 3120 rpm (60s * 26 pulses/0.5s).
The increment size of 120rpm limits the accuracy of measurement.
If the parameter Rate were= 1000 ms, the measurement’s accuracy would be limited by the increment size of 60rpm.
Notes:
The “Cycle duration” function should be used to measure low RPM with high precision.
Frequency can then be calculated using the following formula:
RPM = 60 / T
In this case, this RPM is NOT average RPM; it is instantaneous RPM.
The KBox will wait until the cycle measurement is finished before sending a CAN message with the duration. If the cycle duration is long, the messages may be sent slower than what is selected as the Rate.
RateIf the Cycle duration is shorter than the time between messages set by the Rate, the duration will be re-calculated before being sent.
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