“ENC input (frequency)” | ModuleIdent 0x1809C8
This module provides a frequency measurement. This information can also be used for speed or rotary speed measurement.
The following limit values apply to the determination of the measured values:
Measured value output | Lower measured value limit | Upper measured value limit |
|---|---|---|
“Frequency Value“ | 1 Hz | 1 kHz |
The frequency module provides the following features:
- Parameterizable input characteristics
- Parameterizable frequency output
Fig.31: Settings for the digital input for frequency measurementParameterizable input characteristics
The digital input can be interpreted as having a positive or ground switching characteristic.
This is defined under:
0x80n1:1D “Counter Mode” (n = 1 for ENC 1, n = 3 for ENC 2, n = 5 for ENC 3, n = 7 for ENC 4):
Measurement of frequency/rotary speed | Positive switching | |
|---|---|
0x80n0:1D „Counter Mode“ | Positive Switching (PNP) |
Signal voltage “0” | -3…+1.5 V DC |
Signal voltage “1” | 2.7…28 V DC |
Measurement of frequency/rotary speed | Ground switching | |
|---|---|
0x80n0:1D „Counter Mode“ | Ground Switching (NPN) |
Signal voltage “0” | 2.5…28 V DC |
Signal voltage “1” | -3…+1 V DC |
In this operation mode, an additional pull-up resistor is connected to V+. | |
 | Sensors with open collector output circuits A sensor with an open collector output circuit corresponds to the “Input Type”: “Ground Switching (NPN)”.
|
Parameterizable frequency output (“Frequency value”)
- During frequency measurement, the time between two rising edges at the digital input is measured with a resolution of 40 µs.
- The last period within each PLC cycle is considered, and the corresponding reciprocal is calculated.
- “Frequency Scaling” (index 0x80n0:13) specifies the resolution of the output frequency.
The default value is 1 Hz.
The frequency can also be output in units of 0.1 Hz, 0.01 Hz, or 1 RPM. - If “RPM” is chosen as the output, the number of expected pulses per revolution must also be specified in index 0x80n0:19 as “Pulses per Revolution”.
- In general, the following calculation rule is defined:
- If no full period is detected within a PLC cycle (two positive edges of input n), the last valid value is output.
- The measurement continues across cycles. As soon as a new value is available, the “Frequency Value” process data value is updated.
- If no full period is detected within 1.25 s, the measurement is discarded and the output in the “Frequency Value” process data value is set to the minimum value “0”.
