SP1 configuration (number of Teeth and Prescaler)

Categories: Common Issues, Installation

Something that causes many misunderstandings to new users regarding the SP1 configuration is the confguration of number of teeth and prescaler due to the fact that the SP1 does not syncrhonize these settings with the PC (the SP1 will not send this information during the connection process and then the PC will not be able to synchronize it). Then it is necessary:

  • Ensure that the connection between the PC and the SP1 is established before configure these settings
  • Configure the Number of Teeth and prescaler. For our stock gear it is Teeth=16 and Prescaler=1 (in most cases). Note that this configuration is only valid for rollers over 320 mm and max speed below 225 km/h! (max roller speed 3750 rpm). For higher speeds use the “auto” setting, which will set the prescaler to 4 to avoid problems. Please check the table below
  • Press the “disquette” button, or press OK and reply “YES” to the question “do you want to send the new settings?”
  • Verify that the SP1 LCD shows the stored value (this lasts only 2 or 3 seconds)

** Note: we are testing a new firmware which implements the same synchronization as SP1+, SP5 and SP6. This FW could be used in all SP1 V4 units

AUTOMATIC Prescaler Selection:

When the “auto” setting is ON, the software will select

  • Teeth: 1 to 12: prescaler = 1
  • Teeth: 13 to 49: prescaler = 4 (note that for our stock 16T gear it will chose prescaler=4, which can reduce the accuracy at low speeds)
  • Teeth: 50 or more: prescaler = 16

Manual Prescaler Selection

In general when SP1 is used with our stock 16T gear, number of Teeth = 16 and prescaler = 1, but only for rollers over 320 mm diameter and top speed below 225 km/h. For lower diameters or higher speeds prescaler should be 4

As maximum SP1 input is 1000 pulses per second, the user should ensure that the top frequency is not overpassed using the following formula:

Max Freq = Max Roller RPM / 60 * Teeth / prescaler

(Max Roller RPM = Max Speed (km/h) / 3.6 / (diameter_mm / 1000) * 3.1416) * 60)


For instance for a 320 mm roller running Max Roller RPM at 225 km/h is: Max Roller RPM = 225 / 3.6 / (0.320 * 3.1416) * 60 = 3730 RPM

And for 16T and prescaler = 1 Max Freq = 3730 / 60 * 16 / 1 = 994 Hz

Then for higher speeds (over 225 kmh) or lower roller diameters (below 320 mm) the prescaler should be 4 as in the automatic mode.

For the rest of combinations, say teeth 80 normally there is no need to do any calculation. The 16T is a little more problematic because it is in the border between prescaler=1 and prescaler=4, but it was selected as stock gear because it provides more pulses for the braked dynamometers.

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