Sample rates and accuracy
When using the performance monitor its very important to set the input sample rate appropriately, if they are incorrect, then the results generated by the performance monitor system will be incorrect. for most types of test it is the speed and distance which are the most important parameters, typically the speed and distance should be set to the highest frequency, on a GPS only configuration this is 20Hz, if using accelerometers or a full INS solution this is 200Hz. Just as importantly, the speed and distance update rates should be set ot be the same.
Information on setting up the SPEEDBOX output data rates can be found here.
For reference, internally the performance monitor software takes the input data at the rate set on the hardware and then for calculations it upsamples it to 10kHz (a sample time of 0.1ms). That means there that speed triggers the test, and speed samples are at a rate of 100Hz, then the trigger time is not accurate to just to 10ms, but to 0.1ms. This can be verified with a simple test:
Wait (VAR_0015>15 )
Display "Speed = ", VAR_0015
and then accelerate away to a speed over 15kph (or whatever speed units are set) and the reported speed will be very, very close to 15.
Working with triggers
A common question is how to trigger tests based on the hardware trigger of the SPEEDBOX, the most typical application is starting a test based on a switch connected to a brake pedal switch or laser barrier.
The trigger inputs are available in the performance monitor software as VAR_0350 and VAR_0351:
In the other Race Technology softwares, these varaible simply report a time of the edge, for example "1677.56s", but to allow them to be used in the performance software they are "flags" that got from 0 to 1 for a single system to allow them to trigger a test, most often the code will look something like this:
Wait ( VAR_0350>0.5 )
If this line is added into the script then operation will be halted on this line until the system gets a falling edge, and then continue. As a further example:
Prompt "Waiting for a trigger"
Wait (VAR_0350>0.5 )
StartDist = VAR_0017
in this case the script displays a prompt to the user, waits for the trigger and once the trigger is detected records the speed and distance at that exact time for use later in the script to calculate the results.
Working with sound meters
The performance meters supports up to 2 LxT and 831 serial of sound meters from Larson Davis. To use these meters:
- plug them into the PCs USB ports
- start the performance monitor software
- connect to the data source in the normal way, eg using the USB on the SPEEDBOX
- if you check in the table of live data there will be the SPL and the max SPL from the sound meters
- the SPL and max SPL are also available as variables for use in scripts etc:
If the data is not shown as expected then there maybe an issue with communications, to correct this go to the menu and select "Reset sounds meters"
This will reset the communications to the sound meters and the maximum sound level. If this still doesn't work, it might be required to remove and plug the sound meters USB into the PC, or even plug the sound meter into a different USB port to force the PC to reset the communications.
Note that the "reset sound meters" function is also called at the start of every script.