Measurement SG 1/4-Bridge (quarter bridge) 2/3-wire connection

Notes

Quarter-bridge measurement in 2-wire operation is not recommended in practice. The normal copper supply cables with their own resistance (e.g. ~17 mΩ/m with 1 mm² wire) and their very high temperature sensitivity (~4000 ppm/K, ~0.4%/K) have a considerable effect on the calculation and can only be corrected by continuous offset and gain adjustment. Only 3-wire operation should be used.
Specifications apply to 5 V excitation.
The specification deteriorates at lower excitation voltage; Beckhoff does not have detailed information on this.
If a lower excitation voltage is desired for reasons of sensor self-heating, the excitation voltage can be temporarily switched on/off for non-continuous measurements (clocked operation). Switching on/off must be done from the controller via ADS access to the CoE 0x80n0:02.
Specifications only apply when using wire end sleeves and for cross-sections of 0.5 mm² or more. For smaller cross-sections, increased transition resistance is to be expected.
Avoid repeated insertion/extraction of the push-in connectors in quarter-bridge operation since this may increase the transition resistance.
Integrated supply: 2...5V adjustable, max. supply/excitation 21 mA (internal electronic overload protection).
Note: effectively only half the voltage is present at the quarter-bridge due to the internally switched bridge supplement.

To calculate the quarter-bridge:

Measurement SG 1/4-Bridge (quarter bridge) 2/3-wire connection 1: — Connection of the quarter bridge

Explanation:

R1: external quarter-bridge resistor, nominally 120/350/1000 Ω
R2: internal supplementary resistor, is set to the same value as R1 after the CoE setting "Interface", and is therefore also 120, 350 or 1000 Ω
R3, R4: high-resistance internal bridge supplementary resistors, therefore, do not significantly load the internal supply
Rs: switchable shunt resistor
SW: internal switch for 2/3-wire operation; open: 3-wire operation

The strain relationship (µStrain, µε) is as follows:

Measurement SG 1/4-Bridge (quarter bridge) 2/3-wire connection 2:

For the quarter-bridge, N=1 always applies.

The relationship between U_Bridge/U_Exc and ∆R₁ is non-linear:

Measurement SG 1/4-Bridge (quarter bridge) 2/3-wire connection 3: — Relationship between UBridge/UExc and ∆R₁

The ELM350x devices apply internal linearization so that the output is already linearized

Measurement SG 1/4-Bridge (quarter bridge) 2/3-wire connection 4:

since the internal calculation is based on U_Exc'.

Measurement mode	StrainGauge/SG ¼-bridge 120 Ω 2/3-wire
	32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Measuring range, nominal	±32 mV/V [corresponds to ±64,000 µε at K=2] 120 ± 15.36 Ω	±8 mV/V [corresponds to ±16,000 µε at K=2] 120 ± 3.84 Ω	±4 mV/V [corresponds to ±8,000 µε at K=2] 120 ± 1.92 Ω	±2 mV/V [corresponds to ±4,000 µε at K=2] 120 ± 0.96 Ω
Measuring range, end value (FSV)	32 mV/V	8 mV/V	4 mV/V	2 mV/V
Measuring range, technically usable	±34.359… mV/V	±8.589… mV/V	±4.294… mV/V	±2.147… mV/V
PDO resolution	24 bit (including sign)
PDO LSB (Extended Range)	0.128 ppm 4.096 nV/V	0.128 ppm 1.024 nV/V	0.128 ppm 0.512 nV/V	0.128 ppm 0.256 nV/V
PDO LSB (Legacy Range)	0.119… ppm 3.814… nV/V	0.119… ppm 0.9535… nV/V	0.119… ppm 0.47675… nV/V	0.119… ppm 0.238375… nV/V

Specific data

Measurement mode		Measuring bridge/StrainGauge SG ¼-bridge 120 Ω 2/3-wire
		32 mV/V	8 mV/V	4 mV/V ⁵⁾ (comp.)	2 mV/V ⁵⁾ (comp.)
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.026 %_FSV < ±260 ppm_FSV < ±8.3 µV/V	< ±0.08 %_FSV < ±800 ppm_FSV < ±6.4 µV/V	< ±0.16 %_FSV < ±1600 ppm_FSV < ±6.4 µV/V	< ±0.32 %_FSV < ±3200 ppm_FSV < ±6.4 µV/V
	incl. Offset	< ±0.1 %_FSV < ±1000 ppm_FSV < ±32.0 µV/V	< ±0.4 %_FSV < ±4000 ppm_FSV < ±32.0 µV/V	< ±0.8 %_FSV < ±8000 ppm_FSV < ±32.0 µV/V	< ±1.6 %_FSV < ±16000 ppm_FSV < ±32.0 µV/V
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. ^{2) 6)}	without Offset	< ±0.1745 %_FSV < ±1745 ppm_FSV < ±55.8 µV/V	< ±0.6015 %_FSV < ±6015 ppm_FSV < ±48.1 µV/V	< ±1.203 %_FSV < ±12030 ppm_FSV < ±48.1 µV/V	< ±2.406 %_FSV < ±24060 ppm_FSV < ±48.1 µV/V
	incl. Offset	< ±0.1995 %_FSV < ±1995 ppm_FSV < ±63.8 µV/V	< ±0.718 %_FSV < ±7180 ppm_FSV < ±57.4 µV/V	< ±1.436 %_FSV < ±14360 ppm_FSV < ±57.4 µV/V	< ±2.872 %_FSV < ±28720 ppm_FSV < ±57.4 µV/V
Offset/Zero point deviation (at 23°C) ⁴⁾	E_Offset	< 960 ppm_FSV	< 3920 ppm_FSV	< 7840 ppm_FSV	< 15680 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 160 ppm	< 440 ppm	< 880 ppm	< 1760 ppm
Non-linearity over the whole measuring range	E_Lin	< 200 ppm_FSV	< 650 ppm_FSV	< 1300 ppm_FSV	< 2600 ppm_FSV
Repeatability, over 24 h, with averaging	E_Rep	< 25 ppm_FSV	< 100 ppm_FSV	< 200 ppm_FSV	< 400 ppm_FSV
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
	Noisedensity@1kHz	< tbd.	< tbd.	< tbd.	< tbd.
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
Common-mode rejection ratio (without filtering) ³⁾		tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾		tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.	Tc_Gain	< 20 ppm/K	< 48 ppm/K	< 96 ppm/K	< 192 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 50 ppm_FSV /K < 1.60 µV/V/K	< 180 ppm_FSV /K < 1.44 µV/V/K	< 360 ppm_FSV /K < 1.44 µV/V/K	< 720 ppm_FSV /K < 1.44 µV/V/K
Largest short-term deviation during a specified electrical interference test		tbd. %_FSV	tbd. %_FSV	tbd. %_FSV	tbd. %_FSV
Input impedance ±Input 1	Differential	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1	CommonMode	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 2	3-wire
	Differential	tbd.	tbd.	tbd.	tbd.
	CommonMode	tbd.	tbd.	tbd.	tbd.

Measurement mode	StrainGauge/SG ¼-bridge 350 Ω 2/3-wire
	32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Measuring range, nominal	±32 mV/V [corresponds to ±64,000 µε at K=2] 350 ± 44.8 Ω	±8 mV/V [corresponds to ±16,000 µε at K=2] 350 ± 11.2 Ω	±4 mV/V [corresponds to ±8,000 µε at K=2] 350 ± 5.6 Ω	±2 mV/V [corresponds to ±4,000 µε at K=2] 350 ± 2.8 Ω
Measuring range, end value (FSV)	32 mV/V	8 mV/V	4 mV/V	2 mV/V
Measuring range, technically usable	±34.359… mV/V	±8.589… mV/V	±4.294… mV/V	±2.147… mV/V
PDO resolution	24 bit (including sign)
PDO LSB (Extended Range)	0.128 ppm 4.096 nV/V	0.128 ppm 1.024 nV/V	0.128 ppm 0.512 nV/V	0.128 ppm 0.256 nV/V
PDO LSB (Legacy Range)	0.119… ppm 3.814… nV/V	0.119… ppm 0.9535… nV/V	0.119… ppm 0.47675… nV/V	0.119… ppm 0.238375… nV/V

Specific data

Measurement mode		Measuring bridge/StrainGauge SG ¼-bridge 350 Ω 2/3-wire
		32 mV/V	8 mV/V	4 mV/V ⁵⁾ (comp.)	2 mV/V ⁵⁾ (comp.)
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.022 %_FSV < ±220 ppm_FSV < ±7.0 µV/V	< ±0.08 %_FSV < ±800 ppm_FSV < ±6.4 µV/V	< ±0.16 %_FSV < ±1600 ppm_FSV < ±6.4 µV/V	< ±0.32 %_FSV < ±3200 ppm_FSV < ±6.4 µV/V
	incl. Offset	< ±0.1 %_FSV < ±1000 ppm_FSV < ±32.0 µV/V	< ±0.4 %_FSV < ±4000 ppm_FSV < ±32.0 µV/V	< ±0.8 %_FSV < ±8000 ppm_FSV < ±32.0 µV/V	< ±1.6 %_FSV < ±16000 ppm_FSV < ±32.0 µV/V
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. ^{2) 6)}	without Offset	< ±0.106 %_FSV < ±1060 ppm_FSV < ±33.9 µV/V	< ±0.395 %_FSV < ±3950 ppm_FSV < ±31.6 µV/V	< ±0.79 %_FSV < ±7900 ppm_FSV < ±31.6 µV/V	< ±1.5795 %_FSV < ±15795 ppm_FSV < ±31.6 µV/V
	incl. Offset	< ±0.144 %_FSV < ±1440 ppm_FSV < ±46.1 µV/V	< ±0.5565 %_FSV < ±5565 ppm_FSV < ±44.5 µV/V	< ±1.113 %_FSV < ±11130 ppm_FSV < ±44.5 µV/V	< ±2.2255 %_FSV < ±22255 ppm_FSV < ±44.5 µV/V
Offset/Zero point deviation (at 23°C) ⁴⁾	E_Offset	< 970 ppm_FSV	< 3920 ppm_FSV	< 7840 ppm_FSV	< 15680 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 120 ppm	< 380 ppm	< 760 ppm	< 1520 ppm
Non-linearity over the whole measuring range	E_Lin	< 180 ppm_FSV	< 750 ppm_FSV	< 1500 ppm_FSV	< 3000 ppm_FSV
Repeatability, over 24 h, with averaging	E_Rep	< 25 ppm_FSV	< 100 ppm_FSV	< 200 ppm_FSV	< 400 ppm_FSV
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
	Noisedensity@1kHz	< tbd.	< tbd.	< tbd.	< tbd.
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
Common-mode rejection ratio (without filtering) ³⁾		tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾		tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.	Tc_Gain	< 12 ppm/K	< 50 ppm/K	< 100 ppm/K	< 200 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 30 ppm_FSV /K < 0.96 µV/V/K	< 110 ppm_FSV /K < 0.88 µV/V/K	< 220 ppm_FSV /K < 0.88 µV/V/K	< 440 ppm_FSV /K < 0.88 µV/V/K
Largest short-term deviation during a specified electrical interference test		tbd. %_FSV	tbd. %_FSV	tbd. %_FSV	tbd. %_FSV
Input impedance ±Input 1	Differential	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1	CommonMode	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 2	3-wire
	Differential	tbd.	tbd.	tbd.	tbd.
	CommonMode	tbd.	tbd.	tbd.	tbd.

Measurement mode	StrainGauge/SG 1/4 Bridge 1 kΩ (2/3 wire)
Measurement mode	32 mV/V FSV	8 mV/V FSV	4 mV/V FSV ⁵⁾ (comp.)	2 mV/V FSV ⁵⁾ (comp.)
Measuring range, nominal	±32 mV/V [corresponds to ±64,000 µε at K=2] 1000 ± 128 Ω	±8 mV/V [corresponds to ±16,000 µε at K=2] 1000 ± 32 Ω	±4 mV/V [corresponds to ±8,000 µε at K=2] 1000 ± 16 Ω	±2 mV/V [corresponds to ±4,000 µε at K=2] 1000 ± 8 Ω
Measuring range, end value (FSV)	32 mV/V 128 Ω	8 mV/V 32 Ω	4 mV/V 16 Ω	2 mV/V 8 Ω
Measuring range, technically usable	±34.359... mV/V	±8.589... mV/V	±4.294... mV/V	±2.147... mV/V
PDO resolution	24 Bit (incl. sign)
PDO LSB (Extended Range)	0.128 ppm 4.096 nV/V	0.128 ppm 1.024 nV/V	0.128 ppm 0.512 nV/V	0.128 ppm 0.256 nV/V
PDO LSB (Legacy Range)	0.119… ppm 3.814.. nV/V	0.119… ppm 0.9535 nV/V	0.119… ppm 0.47675 nV/V	0.119… ppm 0.238375 nV/V

Specific data

Measurement mode		Measuring bridge/StrainGauge SG ¼-bridge 1 kΩ 2/3-wire
		32 mV/V	8 mV/V	4 mV/V ⁵⁾ (comp.)	2 mV/V ⁵⁾ (comp.)
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.02 %_FSV < ±200 ppm_FSV < ±6.4 µV/V	< ±0.065 %_FSV < ±650 ppm_FSV < ±5.2 µV/V	< ±0.13 %_FSV < ±1300 ppm_FSV < ±5.2 µV/V	< ±0.26 %_FSV < ±2600 ppm_FSV < ±5.2 µV/V
	incl. Offset	< ±0.1 %_FSV < ±1000 ppm_FSV < ±32.0 µV/V	< ±0.4 %_FSV < ±4000 ppm_FSV < ±32.0 µV/V	< ±0.8 %_FSV < ±8000 ppm_FSV < ±32.0 µV/V	< ±1.6 %_FSV < ±16000 ppm_FSV < ±32.0 µV/V
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. ^{2) 6)}	without Offset	< ±0.1975 %_FSV < ±1975 ppm_FSV < ±63.2 µV/V	< ±0.7435 %_FSV < ±7435 ppm_FSV < ±59.5 µV/V	< ±1.4865 %_FSV < ±14865 ppm_FSV < ±59.5 µV/V	< ±2.973 %_FSV < ±29730 ppm_FSV < ±59.5 µV/V
	incl. Offset	< ±0.2205 %_FSV < ±2205 ppm_FSV < ±70.6 µV/V	< ±0.8415 %_FSV < ±8415 ppm_FSV < ±67.3 µV/V	< ±1.683 %_FSV < ±16830 ppm_FSV < ±67.3 µV/V	< ±3.366 %_FSV < ±33660 ppm_FSV < ±67.3 µV/V
Offset/Zero point deviation (at 23°C) ⁴⁾	E_Offset	< 980 ppm_FSV	< 3940 ppm_FSV	< 7880 ppm_FSV	< 15760 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 105 ppm	< 305 ppm	< 610 ppm	< 1220 ppm
Non-linearity over the whole measuring range	E_Lin	< 165 ppm_FSV	< 560 ppm_FSV	< 1120 ppm_FSV	< 2240 ppm_FSV
Repeatability, over 24 h, with averaging	E_Rep	< 25 ppm_FSV	< 120 ppm_FSV	< 240 ppm_FSV	< 480 ppm_FSV
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
	Noisedensity@1kHz	< tbd.	< tbd.	< tbd.	< tbd.
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	E_{Noise, RMS}	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V	< tbd. ppm_FSV < tbd. digits < tbd. µV/V
	Max. SNR	> tbd. dB	> tbd. dB	> tbd. dB	> tbd. dB
Common-mode rejection ratio (without filtering) ³⁾		tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾		tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.	Tc_Gain	< 13 ppm/K	< 25 ppm/K	< 50 ppm/K	< 100 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 60 ppm_FSV /K < 1.92 µV/V/K	< 230 ppm_FSV /K < 1.84 µV/V/K	< 460 ppm_FSV /K < 1.84 µV/V/K	< 920 ppm_FSV /K < 1.84 µV/V/K
Largest short-term deviation during a specified electrical interference test		tbd. %_FSV	tbd. %_FSV	tbd. %_FSV	tbd. %_FSV
Input impedance ±Input 1	Differential	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1	CommonMode	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 2	3-wire
	Differential	tbd.	tbd.	tbd.	tbd.
	CommonMode	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.

⁴) The offset specification does not apply to 2-wire operation, since the offset is increased on the device side. Therefore, a system-side offset adjustment is recommended, see Tare- or ZeroOffset function. The final targeting basic acuuracy within the 2-wire operation is mainingly dependent by the quality of this system-side offset adjustment.

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 (T_ambient). In real use, for example at a relatively constant ambient temperature T_ambient, 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.

Notice

Transition resistances of the connection contacts

The transition resistance values of the connection contacts affect the measurement. The measuring accuracy can be further increased by a user-side adjustment with the signal connection plugged in.

The temperature sensitivity of the terminal and thus of the measurement setup can be reduced if an external, more temperature-stable supplementary resistor is used for operation of the terminal in half-bridge or even full-bridge mode instead of the internal supplementary resistor for quarter-bridge mode.