Measurement SG 1/1 bridge (full bridge) 4/6-wire connection
Some notes to ELM350x full bridge measurement:
The nominal/technical measuring range is specified in "mV/V"; the maximum permitted supply voltage is 5 V. The maximum nominal measuring range that can be used for the bridge voltage is therefore ±32 mV/V ⋅ 5 V = ±160 mV; the internal circuits are configured accordingly.
The internal measurement is ratiometric, i.e. the feed voltage and the bridge voltage are not measured absolutely, but as a ratio.
The integrated supply can be used as power supply. An external supply is permitted, as long as 5 V is not exceeded.
The terminal has "real" and "compensated" measuring ranges:
- A "real" measuring range measures electrically as specified e.g., in the range 4 mV/V.
- A "compensated" measuring range helps in applications with a small signal (amplitude) and at the same time a high offset component. It measures in a fixed electrical range (i.e., subject to its electrical specification) and performs a "digital zoom", i.e., increases the resolution. The offset must be eliminated by the integrated ZeroOffset function of the terminal.
The following is the specification given for the 6 wire connection. External line resistances are compensated by the 6 wire connection and the full bridge is detected directly from the measuring channel.
In the 4 wire connection, the terminal generally has the same specification, but its view of the connected full bridge is clouded by the unclear and temperature-dependent lead resistances within cables and connectors. In this respect, the overall system "full bridge + leads + measurement channel" will practically not achieve specification values given below.
The lead resistances (cables, connectors, ...) have an effect especially on the gain error, also depending on the temperature. The gain error can be estimated by:
(R+uv (1 + ∆T ⋅ TcCu) + R-uv(1 + ∆T ⋅ TcCu) )/Rnom with TcCu~3930 ppm/K, Rnom
e.g. 350 Ω and R+uv or R-uv lead resistances respectively.
The use of the measurement channel in the 6 wire connection is recommended, especially when significant resistors such as a lightning arrester are put into the line.
By a user-side adjustment with a connected bridge sensor, the measurement uncertainity related to gain and offset error can be significant reduced.
The integrated switcheable shunt resistor can be used to generate a predictable detuning or, in case of deviation, a correction factor.
Note: specifications apply for 5 V SG excitation and symmetric 350R SG.
Note: data are valid from production week 01/ 2019 and
- for ELM3502: HW03
- for ELM3504: HW04
Full bridge calculation:
The strain relationship (µStrain, µε) is as follows:
Measurement mode |
Measuring bridge/StrainGauge SG 1/1-Bridge 4/6-wire | ||||||
---|---|---|---|---|---|---|---|
|
32 mV/V |
8 mV/V
|
4 mV/V |
2 mV/V |
4 mV/V (comp.) 5)
|
2 mV/V (comp.) 5) | |
Integrated power supply |
1…5V adjustable, max. supply/Excitation 21 mA (internal electronic overload protection) therefore | ||||||
Measuring range, nominal |
-32 … +32 mV/V |
-8 … +8 mV/V |
-4 … +4 mV/V |
-2 … +2 mV/V |
-4 … +4 mV/V |
-2 … +2 mV/V | |
Measuring range, end value (FSV) |
32 mV/V |
8 mV/V |
4 mV/V |
2 mV/V |
4 mV/V |
2 mV/V | |
Measuring range, technically usable |
-34.359 … +34.359 mV/V |
-8.590 … +8.590 mV/V |
-4.295 … +4.295 mV/V |
-2.147 … +2.147 mV/V |
-4.295 … +4.295 mV/V |
-2.147 … +2.147 mV/V | |
PDO resolution |
24 bit (including sign) | ||||||
PDO LSB (Extended Range) |
0.128 ppm | ||||||
PDO LSB (Legacy Range) |
0.119… ppm | ||||||
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. 2) |
without Offset |
< ±0.003 %FSV
|
< ±0.006 %FSV
|
< ±0.0085 %FSV
|
< ±0.013 %FSV
|
< ±0.012 %FSV
|
< ±0.024 %FSV
|
incl. Offset |
< ±0.0075 %FSV
|
< ±0.015 %FSV
|
< ±0.03 %FSV
|
< ±0.06 %FSV
|
< ±0.03 %FSV
|
< ±0.06 %FSV
| |
Extended basic accuracy: Measuring deviation At 0…55°C, with averaging, typ. 2) 6) |
without Offset |
< ±0.011 %FSV
|
< ±0.028 %FSV
|
< ±0.0515 %FSV
|
< ±0.099 %FSV
|
< ±0.056 %FSV
|
< ±0.1115 %FSV
|
incl. Offset |
< ±0.013 %FSV
|
< ±0.0315 %FSV
|
< ±0.059 %FSV
|
< ±0.115 %FSV
|
< ±0.0625 %FSV
|
< ±0.1245 %FSV
| |
Offset/Zero point deviation (at 23°C) |
EOffset |
< 70 ppmFSV |
< 140 ppmFSV |
< 280 ppmFSV |
< 580 ppmFSV |
< 280 ppmFSV |
< 560 ppmFSV |
Gain/scale/amplification deviation (at 23°C) |
EGain |
< 24 ppm |
< 50 ppm |
< 70 ppm |
< 110 ppm |
< 100 ppm |
< 200 ppm |
Non-linearity over the whole measuring range |
ELin |
< 18 ppmFSV |
< 30 ppmFSV |
< 45 ppmFSV |
< 65 ppmFSV |
< 60 ppmFSV |
< 120 ppmFSV |
Repeatability, over 24 h, with averaging |
ERep |
< 5 ppmFSV |
< 10 ppmFSV |
< 15 ppmFSV |
< 25 ppmFSV |
< 20 ppmFSV |
< 40 ppmFSV |
Common-mode rejection ratio (without filter) 3) |
DC |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
50 Hz |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
1 kHz |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
Common-mode rejection ratio (with 50 Hz FIR filter) 3) |
DC |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
50 Hz |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
1 kHz |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
Temperature coefficient, typ. |
TcGain |
< 2.5 ppm/K |
< 4 ppm/K |
< 5 ppm/K |
< 6 ppm/K |
< 8 ppm/K |
< 16 ppm/K |
TcOffset |
< 2 ppmFSV/K |
< 7.5 ppmFSV/K |
< 15 ppmFSV/K |
< 30 ppmFSV/K |
< 15 ppmFSV/K |
< 30 ppmFSV/K | |
Largest short-term deviation during a specified electrical interference test |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
Input impedance ±Input 1 |
Differential |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
CommonMode |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
Input impedance ±Input 2 |
4-wire |
No usage of this input in this mode | |||||
Differential |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. | |
CommonMode |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
tbd. |
2) In real bridge measurement, an offset adjustment is usually carried out after installation. 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 ELM Features and also ELM Features of the terminal or in the controller by a higher-level tare function. The offset deviation of a bridge measurement 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.
5) The channel measures electrically to 8 mV/V, but displays its measured value scaled to 2 or 4 mV/V. The Compensated function facilitates measurement of low levels even with high offset.
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.
ELM3502 (20 ksps)
Measurement mode | StrainGauge/SG 1/1 Bridge 4/6 wire | ||||
---|---|---|---|---|---|
| 32 mV | 8 mV | 4 mV | 2 mV | |
Noise (without filtering, at 23°C) | ENoise, PtP | < 125 ppmFSV | < 425 ppmFSV | < 1050 ppmFSV | < 1600 ppmFSV |
ENoise, RMS | < 25 ppmFSV | < 70 ppmFSV | < 140 ppmFSV | < 270 ppmFSV | |
Max. SNR | > 92.0 dB | > 83.1 dB | > 77.1 dB | > 71.4 dB | |
Noisedensity@1kHz | < 11.31 | < 7.92 | < 7.92 | < 7.64 | |
Noise (with 50 Hz FIR filtering, at 23°C) | ENoise, PtP | < 12 ppmFSV | < 30 ppmFSV | < 60 ppmFSV | < 120 ppmFSV |
ENoise, RMS | < 2.0 ppmFSV | < 5.0 ppmFSV | < 10.0 ppmFSV | < 20.0 ppmFSV | |
Max. SNR | > 114.0 dB | > 106.0 dB | > 100.0 dB | > 94.0 dB |
ELM3504 (10 ksps)
Measurement mode | StrainGauge/SG 1/1 Bridge 4/6 wire | ||||
---|---|---|---|---|---|
| 32 mV | 8 mV | 4 mV | 2 mV | |
Noise (without filtering, at 23°C) | ENoise, PtP | < 85 ppmFSV | < 300 ppmFSV | < 600 ppmFSV | < 1200 ppmFSV |
ENoise, RMS | < 15 ppmFSV | < 50 ppmFSV | < 100 ppmFSV | < 200 ppmFSV | |
Max. SNR | > 96.5 dB | > 86.0 dB | > 80.0 dB | > 74.0 dB | |
Noisedensity@1kHz | < 6.79 | < 5.66 | < 5.66 | < 5.66 | |
Noise (with 50 Hz FIR filtering, at 23°C) | ENoise, PtP | < 12 ppmFSV | < 30 ppmFSV | < 60 ppmFSV | < 120 ppmFSV |
ENoise, RMS | < 2.0 ppmFSV | < 5.0 ppmFSV | < 10.0 ppmFSV | < 20.0 ppmFSV | |
Max. SNR | > 114.0 dB | > 106.0 dB | > 100.0 dB | > 94.0 dB |