Any suggestions / guidance on how I might optimise this? The arrays contain ~600 elements and this is executed every 500ms to formulate this string which then gets written to a file. Cpu is averaging ~30%.

fun SamplingEvent.DataEvent.SensorArrayValuesEvent.toSensorDataString(): String {
    var segment = ""
    for (i in 0..(sensorCount - 1)) {
        segment += "$timestampNanos,${sensorType[i]},${values0[i]},${values1[i]},${values2[i]},${values3[i]},${values4[i]},${values5[i]}\n"
    }
    return segment.dropLast(1)
}

My first instinct is to lift this out of extension function and use/reuse StringBuilder (with sufficient initial buffer) ?

FYI, you can use `until`:

for (i in 0 until sensorCount) {