Frequency measurement/velocity measurement
The following indices are used for setting the parameters for calculating the frequency or velocity. The determined frequency or velocity is output in index 0x6000:13 "Frequency value" as 32-bit value or 0x6000:1A "Frequency value (int16)" as 16-bit value as process data.
Index (hex) | Name | Meaning | Default |
|---|---|---|---|
8000:0F | Frequency window base | Specifies the unit for the timeframe for the frequency measurement. Two time units (1 µs, 1 ms) are available | 0x00 (1 µs) |
8000:11 | Frequency window | This is the time used for determining the frequency. The number of periods and the analog part (the period resolution) in the timeframe is measured and then divided by the timeframe size. The determined frequency is output as process data
The scaling of the output value is determined by The frequency calculation is carried out locally without distributed clocks function. | 0x2710 (10000dec) |
8000:1D | Frequency numerator | Frequency numerator, used for scaling the frequency, cf. frequency scaling. | 0x00000064 |
8000:1E | Frequency denominator | Frequency denominator value, used for scaling of frequency and velocity calculation, see Frequency scaling and Example for velocity calculation. | 0x0000001 |
8000:1F | Frequency Filter | IIR filter |
|
Frequency scaling
The frequency can be scaled via the two indices 0x8000:1D "Frequency numerator" and 0x8000:1E "Frequency denominator". The entered values yield a fraction. This number must be used as divisor to obtain the unit in hertz, for example:
0x8000:1D "Frequency numerator" = 100
0x8000:1E "Frequency denominatior" = 1
- Fraction: 100
- Output of frequency 100: 0.01 Hz
Since a position encoder with sin/cos interface is an analog output signal, in contrast to digital incremental encoders, not only the whole periods are taken into account for the frequency measurement, but also the analog part of the periods. The period determination is set in CoE, index 0x8001:11 "Analog resolution".
The "Counter Value" (0x6000:11) consists of the period counter and the period portion.
Example: Encoder output: 2048 pulses, 0x8001:11 "Analog resolution": 10 bits
- Process data "Counter Value": 32 bits, number of periods 22 bits, analog part 10 bits,
- A full mechanical revolution corresponds to 360° = 2048*1024 pulses = 2097152 increments (2048 periods)
Example for velocity calculation
The velocity calculation is based on the frequency measurement, which is determined as follows:
f= (S2-S1)/tf | |
|---|---|
f | frequency to be measured. Via index 0x8000:1D "Frequency numerator" the scaling of the frequency can be determined. |
S1 | Counter value at position 1 |
S2 | Counter value at position 2 |
tf | Timeframe for frequency determination, this can be set via index 0x8000:0F "Frequency window base" and index 0x8000:11 "Frequency window". |
The velocity has the following relationship with the frequency:
v = f/a | |
|---|---|
v | velocity to be calculated |
f | measured frequency |
a | Conversion factor [pulses/unit] for the velocity. This is entered in index 0x8000:1D "Frequency numerator" and 0x8000:1E "Frequency denominator" |
The conversion factor a can be determined as follows:
Example for velocity calculation in m/s:
12 mm travel path corresponds to a full mechanical revolution and therefore a "Counter Value" of 2097152 increments (2048 periods).
- a = 2048 periods / 12 mm = 170.666667 periods/mm = 170666.667 periods/m
The output of the measured value essentially depends on the unit in which the frequency is determined and on the unit in which the conversion factor is specified.
Index (hex) | Name | Example for set value | Comment |
|---|---|---|---|
8000:1D | Frequency numerator | 100 | Output of the value in 0.01 Hz |
8000:1E | Frequency denominator | 170666667 | Conversion factor a in pulses/mm |
In this case the velocity is output in index 0x6000:13 "Frequency value" as 32-bit value or 0x6000:1A "Frequency value (int16) as 16-bit value in the following unit:
This means the value must be multiplied by 0.00001 to get the unit in m/s. To get a high resolution of the output value, the values in 0x8000:1D "Frequency numerator" and 0x8000:1E "Frequency denominator" should be specified in the same order of magnitude if possible.
Example for velocity calculation in revolutions/min:
After a full revolution the "Counter Value" is 2048 periods.
- A = 2048 periods / 1 revolution = 2048 periods / revolution
The output of the measured value essentially depends on the unit in which the frequency is determined and on the unit in which the conversion factor is specified.
Index (hex) | Name | Example for set value | Comment |
|---|---|---|---|
8000:1D | Frequency numerator | 6000 | Output of the value in 0.01 rpm |
8000:1E | Frequency denominator | 2048 | Conversion factor in periods/revolution |
In this case the velocity is output in index 0x6000:13 "Frequency value" as 32-bit value or 0x6000:1A "Frequency value (int16)" as 16-bit value in the following unit:
This means the value must be multiplied by 0.01 to get the unit in revolutions/s, or multiplication by 0.6 for revolutions/min.
To get a high resolution of the output value, the values in 0x8000:1D "Frequency numerator" and 0x8000:1E "Frequency denominator" should be specified in the same order of magnitude if possible.