In most of the cases, the analysis will be done with a vibration sensor. Just enable the desired channel in the list on the left upper side of the module setup. Basically, any analog input can be used, here are some examples:
- acceleration sensor
- pressure sensor
- output of the rotational vibration / torsional vibration module
Frequency channel setup
For determining the engine speed (rpm), an RPM sensor is needed. A lot of different sensors are supported:
- Tacho probe (1 pulse/revolution; connect to analog or digital input)
- 36-2 or 60-2 sensor (connect to an analog input)
- Encoder (e.g. 1800 pulses/revolution or CDM-360 / CDM-720 or 60-2; connect to Counter input)
- any RPM channel (e.g. analog voltage or RPM from CAN bus; but then the phase of the harmonics cannot be extracted, because there is no zero-angle information)
Select “Counters” if you connect an Encoder to the Dewesoft instrument Counter input (usually 7pin Lemo connector).
An encoder (e.g. 1800 pulses/revolution) or CDM (CDM-360, CDM-720) or Tacho (digital = TTL levels) or tooth wheel sensor (60-2) can be used. The counter setup in the background is then controlled (locked) by the Order tracking module, the counters will not be accessible (greyed out), to prevent double-usage.
In Counter mode, you can optionally set the filter, to suppress glitches/spikes shorter than the shown value (100ns...5μs). The optimal setting is derived from the following equation:
The biggest error is caused by improper mounting of an encoder. There are different mounting errors using a coupling, such as parallel, skewed, angled. The error will appear as periodic angle/frequency deviation during constant engine speed.
The easiest way is using a tacho probe with digital output. It can be directly connected to the Dewesoft instrument's counter input and is easy to mount. For example, the optical tacho probe only requires a reflective sticker on the rotating part, see picture below.
If you have a tacho probe (1 pulse/rev, optic, magnetic or any other type) with analog output signal, you can just connect it to an analog input (e.g. SIRIUS-ACC module) and use the “analog” setting of the frequency section.
Here example signals of a magnetic and an optic probe are shown.
Beyond that, also 60-2 and 36-2 analog signals from the crank sensor (inside nearly every vehicle) are supported.
Click the “...” button to adjust the correct trigger level. You can also use the “Find” algorithm, which will automatically determine the best possible value. Please take care when using a magnetic probe, that also the induced voltage will change depending on the RPM, resulting in a different trigger level. Therefore perform some test runs across the interesting RPM range to find the best trigger level.
Below, an example of 60-2 analog sensor is shown.
HINT: If machines with highly dynamic rpm, or with a high rotational vibration are analysed (big rpm deviations during one revolution), and also high orders should be extracted, an encoder or a tacho probe with more than one pulse/rev. (180p/rev or higher) is recommended, to get higher accuracy.
Reason: The order tracking algorithm resamples the time domain data into the angle domain. If we get more information from the RPM probe, we have more pulses per revolution and the resampling to the angle domain will be much more accurate!
You can also use any signal or channel as input, which directly represents the RPM (e.g. 0...10V equals 0...5000 rpm).
The disadvantage, however, is, that there is no zero-angle information, and therefore extraction of the phase angles of the single orders is not possible.
Following example shows an RPM signal from CAN bus inside a vehicle (red line). Note that the sampling points are asynchronous. The blue line is the output signal of an acceleration sensor.