Potentiometer measurement
The potentiometer should be supplied with the integrated power supply unit (max. 5 V, configurable). The slider voltage is then measured relative to the supply voltage and output in %. Technical, the measurement is similar to a strain gauge half bridge.
Potentiometers from 1 kΩ can be used.
The following is the specification given for the 5 wire connection. External line resistances are compensated by the 5 wire connection and the potentiometer is detected directly from the measuring channel. In the 3 wire connection, the measurement channel generally has the same specification, as it continues to measure internally in 5 wire mode and bridges internally for this purpose. But its view of the connected potentiometer is clouded by the unclear and temperature-dependent lead resistances within cables and connectors. In this respect, the overall system "potentiometer + leads + measurement channel" in 3 wire mode will then practically not achieve specification values given below.
Diagnostics
- Slider breakage: full-scale deflection or 0 display
- Supply interruption: full-scale deflection or 0 display
Measurement mode | Potentiometer (3/5-wire) |
|---|---|
Operation mode | The supply voltage is configurable via CoE, |
Measuring range, nominal | -1 … 1 V/V |
Measuring range, end value (FSV) | 1 V/V |
Measuring range, technically usable | -1 …1 V/V |
PDO resolution | 24 bit (including sign) |
PDO LSB (Extended Range) | 0.128 ppm |
PDO LSB (Legacy Range) | 0.119… ppm |
Specific data (not valid for ELM3704-1001)
Measurement mode | Potentiometer (3/5-wire) | |||
|---|---|---|---|---|
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. 2) | without Offset | < ± tbd. %FSV | ||
incl. Offset | < ± tbd. %FSV | |||
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. 2) 6) | without Offset | < ± tbd. %FSV | ||
incl. Offset | < ± tbd. %FSV | |||
Offset/Zero point deviation (at 23°C) | EOffset | < tbd. ppmFSV | ||
Gain/scale/amplification deviation (at 23°C) | EGain | < tbd. ppm | ||
Non-linearity over the whole measuring range | ELin | < tbd. ppmFSV | ||
Repeatability, over 24 h, with averaging | ERep | < tbd. ppmFSV | ||
Temperature coefficient, typ. | TcGain | < 2 ppm/K | ||
TcOffset | < tbd. ppmFSV/K < tbd. µV/V/K | |||
Noise (without filtering, at 23°C) | ENoise, PtP | < tbd. ppmFSV | ||
ENoise, RMS | < tbd. ppmFSV | |||
Max. SNR | > tbd. dB | |||
Noisedensity@1kHz | < tbd. | |||
Noise (with 50 Hz FIR filter, at 23°C) | ENoise, PtP | < tbd. ppmFSV | ||
ENoise, RMS | < tbd. ppmFSV | |||
Max. SNR | > tbd. dB | |||
Common-mode rejection ratio (without filter) 3) | DC: | 50 Hz: | 1 kHz: | |
Common-mode rejection ratio (with 50 Hz FIR filter) 3) | DC: | 50 Hz: | 1 kHz: | |
Largest short-term deviation during a specified electrical interference test | tbd. %FSV = tbd. ppmFSV typ. | |||
Input impedance (internal resistance)
| tbd. | |||
typ.
typ.2) A regular offset adjustment with connected potentiometer is recommended. The given offset specification of the terminal is therefore practically irrelevant. Therefore, specification values with and without offset are given here. In practice, the offset component can be eliminated by the functions Tare and also ZeroOffset of the terminal or in the controller by a higher-level tare function. The offset deviation over time can change, therefore Beckhoff recommends a regular offset adjustment or careful observation of the change.
3) Values related to a common mode interference between SGND and internal ground.
6) Calculated value according to equation in chapter "General information on measuring accuracy/measurement uncertainty" for quick estimation of usability over the specified ambient temperature range in operation (Tambient). In real use, for example at a relatively constant ambient temperature Tambient, a lower (better) achievable uncertainty is attained. A specific calculation according to chapter "General information on measuring accuracy/measurement uncertainty" is recommended, especially if the instrument allows a wider ambient temperature range in operation than 0...55 °C.
Potentiometer measurement range
Fig.91: Representation potentiometer measurement range|
Note: In Extended Range Mode the Underrange/Overrange display in the PDO status has the character of an information/warning when the nominal measuring range is exceeded, i.e. no Error is displayed in the PDO status and LED. If the technical measuring range is also exceeded, Error = TRUE is also displayed. The detection limit for Underrange/Overrange Error can be set in the CoE. In Legacy Range mode, an Underrange/Overrange event also leads to an Error in the PDO status. |