Measurement resistance 0…5 kΩ
Note on measuring resistances or resistance ratios
With 2‑wire measurement, the line resistance of the sensor supply lines influences the measured value. If a reduction of this systematic error component is desirable for 2‑wire measurements, the resistance of the supply line to the measuring resistance should be taken into account, in which case the resistance of the supply line has to be determined first.
Taking into account the uncertainty associated with this supply line resistance, it can then be included statically in the calculation, in the EL3751 via 0x8000:13 and in the ELM350x/ ELM370x via 0x80n0:13.
Any change in resistance of the supply line due to ageing, for example, is not taken into account automatically. Just the temperature dependency of copper lines with approx. 4000 ppm/K (corresponds to 0.4%/K!) is not insignificant during 24/7 operation.
A 3‑wire measurement enables the systematic component to be eliminated, assuming that the two supply lines are identical. With this type of measurement, the lead resistance of a supply line is measured continuously. The value determined in this way is then deducted twice from the measurement result, thereby eliminating the line resistance. Technically, this leads to a significantly more reliable measurement. However, taking into account the measurement uncertainty, the gain from the 3‑wire connection is less significant, since this assumption is subject to high uncertainty, in view of the fact that the individual line that was not measured may be damaged, or a varying resistance may have gone unnoticed.
Therefore, although technically the 3‑wire connection is a tried and tested approach, for measurements that are methodological assessed based on measurement uncertainty, we strongly recommend fully‑compensated 4‑wire connection.
With both 2‑wire and 3‑wire connection, the contact resistances of the terminal contacts influence the measuring process. The measuring accuracy can be further increased by a user‑side adjustment with the signal connection plugged in.
Notice | |
Measurement of small resistances Especially for measurements in the range < 10 Ω, the 4‑wire connection is absolutely necessary due to the relatively high supply and contact resistances. It should also be considered that with such low resistances the relative measurement error in relation to the full scale value (FSV) can become high ‑ for such measurements resistance measurement terminals with small measuring ranges such as EL3692 in 4‑wire measurement should be used if necessary. |
Corresponding considerations also lead to the common connection methods in bridge operation:
- Full bridge: 4‑wire connection without line compensation, 6‑wire connection with full line compensation
- Half bridge: 3‑wire connection without line compensation, 5‑wire connection with full line compensation
- Quarter bridge: 2‑wire connection without line compensation, 3‑wire connection with theoretical line compensation and 4‑wire connection with full line compensation
Measurement mode | Electrical resistance | |
|---|---|---|
Operation mode | 2.5 V feed voltage, fixed setting n +Uv 5 kΩ reference resistance at –I2 Supply current is given by: | |
Measuring range, nominal | 0…5 kΩ | |
Measuring range, end value (full scale value) | 5 kΩ | |
Measuring range, technically usable | 0 Ω…5.368 kΩ | |
PDO resolution | 23 bit (unsigned) | |
PDO LSB (Extended Range) | 640 µΩ | |
PDO LSB (Legacy Range) | 596.. µΩ | |
Basic accuracy: Measuring deviation at 23°C, with averaging | 2-wire connection ±0.05% typ. (full scale value) 3-wire connection ±0.03% typ. (full scale value) 4-wire connection ±0.01% typ. (full scale value) | |
Temperature coefficient (Terminal) | TcTerminal | < 10 ppm/K typ. |
Measurement mode | Electrical resistance (2 wire) | ||||
|---|---|---|---|---|---|
Offset/Zero Point deviation (at 23°C) | EOffset | < 475 [ppmFSV] | |||
Gain/scale/amplification deviation (at 23°C) | EGain | < 150 [ppm] | |||
Non-linearity over the whole measuring range | ELin | < 25 [ppmFSV] | |||
Repeatability | ERep | < 20 [ppmFSV] | |||
Noise (without filtering) | ENoise, PtP | < 220 [ppmFSV] | < 1719 [digits] | ||
ENoise, RMS | < 45 [ppmFSV] | < 352 [digits] | |||
Max. SNR | > 86.9 [dB] | ||||
Noisedensity@1kHz | < 3.18 | ||||
Noise (with 50 Hz FIR filtering) | ENoise, PtP | < 12 [ppmFSV] | < 94 [digits] | ||
ENoise, RMS | < 3.0 [ppmFSV] | < 23 [digits] | |||
Max. SNR | > 110.5 [dB] | ||||
Common-mode rejection ratio (without filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Common-mode rejection ratio (with 50 Hz FIR filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Largest short-term deviation during a specified electrical interference test | ±0.1%FSV = ±1000 ppmFSV typ. | ||||
3) Values related to a common mode interference between SGND and internal ground.
Measurement mode | Electrical resistance (3 wire) | ||||
|---|---|---|---|---|---|
Offset/Zero Point deviation (at 23°C) | EOffset | < 280 [ppmFSV] | |||
Gain/scale/amplification deviation (at 23°C) | EGain | < 100 [ppm] | |||
Non-linearity over the whole measuring range | ELin | < 25 [ppmFSV] | |||
Repeatability | ERep | < 20 [ppmFSV] | |||
Noise (without filtering) | ENoise, PtP | < 185 [ppmFSV] | < 1445 [digits] | ||
ENoise, RMS | < 35 [ppmFSV] | < 273 [digits] | |||
Max. SNR | > 89.1 [dB] | ||||
Noisedensity@1kHz | < 2.47 | ||||
Noise (with 50 Hz FIR filtering) | ENoise, PtP | < 11 [ppmFSV] | < 86 [digits] | ||
ENoise, RMS | < 3.0 [ppmFSV] | < 23 [digits] | |||
Max. SNR | > 110.5 [dB] | ||||
Common-mode rejection ratio (without filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Common-mode rejection ratio (with 50 Hz FIR filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Largest short-term deviation during a specified electrical interference test | ±0.1%FSV = 1000 ppmFSV typ. | ||||
3) Values related to a common mode interference between SGND and internal ground.
Measurement mode | Electrical resistance (4 wire) | ||||
|---|---|---|---|---|---|
Offset/Zero Point deviation (at 23°C) | EOffset | < 70 [ppmFSV] | |||
Gain/scale/amplification deviation (at 23°C) | EGain | < 70 [ppm] | |||
Non-linearity over the whole measuring range | ELin | < 15 [ppmFSV] | |||
Repeatability | ERep | < 10 [ppmFSV] | |||
Noise (without filtering) | ENoise, PtP | < 155 [ppmFSV] | < 1211 [digits] | ||
ENoise, RMS | < 30 [ppmFSV] | < 234 [digits] | |||
Max. SNR | > 90.5 [dB] | ||||
Noisedensity@1kHz | < 2.12 | ||||
Noise (with 50 Hz FIR filtering) | ENoise, PtP | < 9 [ppmFSV] | < 70 [digits] | ||
ENoise, RMS | < 3.0 [ppmFSV] | < 23 [digits] | |||
Max. SNR | > 110.5 [dB] | ||||
Common-mode rejection ratio (without filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Common-mode rejection ratio (with 50 Hz FIR filtering)3 | DC: | 50 Hz: | 1 kHz: | ||
Largest short-term deviation during a specified electrical interference test | ±0.1% = 1000 ppmFSV typ. | ||||
3) Values related to a common mode interference between SGND and internal ground.
Resistance measurement range 5 kΩ
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Note: The channel also works in electrically bipolar mode and records negative values in the unipolar measuring ranges (measurement from 0 V, 0 mA, 4 mA, 0 Ω). This enables the channel to provide a precise diagnosis even with signals < 0. In these measuring ranges the limit value for the "Underrange Error" in Extended Mode is -1% of the full scale value (FSV). The limit value can be set in CoE object 0x80n0:32. This avoids irritating error messages if the channel is not wired (e.g. without sensor) or the electrical signal fluctuates slightly around zero. The process data value of 0x00000000 is not undershot. If the "UnderrangeError" detection is to be set even less sensitive, the magnitude of the negative limit value in the CoE object referred to above can be set even higher. |
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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. |