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.

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.

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 EPP3504‑0023 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 1/4-bridge 120 Ω 2/3-wire
Measurement mode	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

Preliminary specifications:

Measurement mode			StrainGauge/SG 1/4-bridge 120 Ω 2/3-wire
Measurement mode			32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾		without Offset	< ±0.052%_FSV < ±520 ppm_FSV < ±16.6 µV/V	< ±0.16%_FSV < ±1600 ppm_FSV < ±12.8 µV/V	< ±0.32%_FSV < ±3200 ppm_FSV < ±12.8 µV/V	< ±0.64%_FSV < ±6400 ppm_FSV < ±12.8 µV/V
		with Offset	< ±0.2%_FSV < ±2000 ppm_FSV < ±64 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
Offset/Zero point deviation (at 23°C) ⁴⁾		E_Offset	< 1920 ppm_FSV	< 7840 ppm_FSV	< 15680 ppm_FSV	< 31360 ppm_FSV
Gain/scale/amplification deviation (at 23°C)		E_Gain	< 320 ppm	< 880 ppm	< 1760 ppm	< 3520 ppm
Non-linearity over the whole measuring range		E_Lin	< 400 ppm_FSV	< 1300 ppm_FSV	< 2600 ppm_FSV	< 5200 ppm_FSV
Repeatability (at 23°C)		E_Rep	< 50 ppm_FSV	< 200 ppm_FSV	< 400 ppm_FSV	< 800 ppm_FSV
Common-mode rejection ratio (without filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.		Tc_Gain	< 40 ppm/K	< 96 ppm/K	< 192 ppm/K	< 384 ppm/K
Temperature coefficient, typ.		Tc_Offset	< 100 ppm_FSV/K < 3.2 µV/V/K	< 360 ppm_FSV/K < 2.88 µV/V/K	< 720 ppm_FSV/K < 2.88 µV/V/K	< 1440 ppm_FSV/K < 2.88 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.

Noise (with/ without filtering)/ preliminary data:

Measurement mode		StrainGauge/SG 1/4-bridge 120 Ω 2/3-wire
Measurement mode		32 mV/V	8 mV/V	4 mV/V (comp.)⁵⁾	2 mV/V (comp.)⁵⁾
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 285.0 ppm_FSV < 2227 digits < 9.12 µV/V	< 1000.0 ppm_FSV < 7813 digits < 8.0 µV/V	< 2000.0 ppm_FSV < 15625 digits < 8.0 µV/V	< 4000.0 ppm_FSV < 31250 digits < 8.0 µV/V
	E_{Noise, RMS}	< 50.0 ppm_FSV < 391 digits < 1.6 µV/V	< 150.0 ppm_FSV < 1172 digits < 1.2 µV/V	< 300.0 ppm_FSV < 2344 digits < 1.2 µV/V	< 600.0 ppm_FSV < 4688 digits < 1.2 µV/V
	Max. SNR	> 86.0 dB	> 76.5 dB	> 70.5 dB	> 64.4 dB
	Noisedensity@1kHz	< 0.02	< 0.02	< 0.02	< 0.02
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< 20.0 ppm_FSV < 156 digits < 0.64 µV/V	< 60.0 ppm_FSV < 469 digits < 0.48 µV/V	< 120.0 ppm_FSV < 938 digits < 0.48 µV/V	< 240.0 ppm_FSV < 1875 digits < 0.48 µV/V
	E_{Noise, RMS}	< 4.0 ppm_FSV < 31 digits < 0.13 µV/V	< 12.0 ppm_FSV < 94 digits < 0.1 µV/V	< 24.0 ppm_FSV < 188 digits < 0.1 µV/V	< 48.0 ppm_FSV < 375 digits < 0.1 µV/V
	Max. SNR	> 108.0 dB	> 98.4 dB	> 92.4 dB	> 86.4 dB

Measurement mode	StrainGauge/SG 1/4-bridge 350 Ω 2/3-wire
Measurement mode	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

Preliminary specifications:

Measurement mode			StrainGauge/SG 1/4-bridge 350 Ω 2/3-wire
Measurement mode			32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾		without Offset	< ±0.044%_FSV < ±440 ppm_FSV < ±14 µV/V	< ±0.16%_FSV < ±1600 ppm_FSV < ±12.8 µV/V	< ±0.32%_FSV < ±3200 ppm_FSV < ±12.8 µV/V	< ±0.64%_FSV < ±6400 ppm_FSV < ±12.8 µV/V
		with Offset	< ±0.2%_FSV < ±2000 ppm_FSV < ±64 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
Offset/Zero point deviation (at 23°C) ⁴⁾		E_Offset	< 1940 ppm_FSV	< 7840 ppm_FSV	< 15680 ppm_FSV	< 31360 ppm_FSV
Gain/scale/amplification deviation (at 23°C)		E_Gain	< 240 ppm	< 760 ppm	< 1520 ppm	< 3040 ppm
Non-linearity over the whole measuring range		E_Lin	< 360 ppm_FSV	< 1500 ppm_FSV	< 3000 ppm_FSV	< 6000 ppm_FSV
Repeatability (at 23°C)		E_Rep	< 50 ppm_FSV	< 200 ppm_FSV	< 400 ppm_FSV	< 800 ppm_FSV
Common-mode rejection ratio (without filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.		Tc_Gain	< 24 ppm/K	< 100 ppm/K	< 200 ppm/K	< 400 ppm/K
Temperature coefficient, typ.		Tc_Offset	< 60 ppm_FSV/K < 1.92 µV/V/K	< 220 ppm_FSV/K < 1.76 µV/V/K	< 440 ppm_FSV/K < 1.76 µV/V/K	< 880 ppm_FSV/K < 1.76 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.

Noise (with/ without filtering)/ preliminary data:

Measurement mode		StrainGauge/SG 1/4-bridge 350 Ω 2/3-wire
		32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 290.0 ppm_FSV < 2266 digits < 9.28 µV/V	< 1000.0 ppm_FSV < 7813 digits < 8.0 µV/V	< 2000.0 ppm_FSV < 15625 digits < 8.0 µV/V	< 4000.0 ppm_FSV < 31250 digits < 8.0 µV/V
	E_{Noise, RMS}	< 50.0 ppm_FSV < 391 digits < 1.6 µV/V	< 160.0 ppm_FSV < 1250 digits < 1.28 µV/V	< 320.0 ppm_FSV < 2500 digits < 1.28 µV/V	< 640.0 ppm_FSV < 5000 digits < 1.28 µV/V
	Max. SNR	> 86.0 dB	> 75.9 dB	> 69.9 dB	> 63.9 dB
	Noisedensity@1kHz	< 0.02	< 0.02	< 0.02	< 0.02
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< 15.0 ppm_FSV < 117 digits < 0.48 µV/V	< 50.0 ppm_FSV < 391 digits < 0.4 µV/V	< 100.0 ppm_FSV < 781 digits < 0.4 µV/V	< 200.0 ppm_FSV < 1563 digits < 0.4 µV/V
	E_{Noise, RMS}	< 3.0 ppm_FSV < 23 digits < 0.1 µV/V	< 9.0 ppm_FSV < 70 digits < 0.07 µV/V	< 18.0 ppm_FSV < 141 digits < 0.07 µV/V	< 36.0 ppm_FSV < 281 digits < 0.07 µV/V
	Max. SNR	> 110.5 dB	> 100.9 dB	> 94.9 dB	> 88.9 dB

Measurement mode	StrainGauge/SG 1/4-bridge 1 kΩ 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] 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 (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

Preliminary specifications:

Measurement mode			StrainGauge/SG 1/4-bridge 1 kΩ 2/3-wire
			32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾		without Offset	< ±0.04%_FSV < ±400 ppm_FSV < ±12.8 µV/V	< ±0.13%_FSV < ±1300 ppm_FSV < ±10.4 µV/V	< ±0.26%_FSV < ±2600 ppm_FSV < ±10.4 µV/V	< ±0.52%_FSV < ±5200 ppm_FSV < ±10.4 µV/V
		with Offset	< ±0.2%_FSV < ±2000 ppm_FSV < ±64 µV/V	< ±0.4%_FSV < ±4000 ppm_FSV < ±32 µV/V	< ±0.8%_FSV < ±8000 ppm_FSV < ±32 µV/V	< ±1.6%_FSV < ±16000 ppm_FSV < ±32 µV/V
Offset/Zero point deviation (at 23°C) ⁴⁾		E_Offset	< 1960 ppm_FSV	< 7880 ppm_FSV	< 15760 ppm_FSV	< 31520 ppm_FSV
Gain/scale/amplification deviation (at 23°C)		E_Gain	< 210 ppm	< 610 ppm	< 1220 ppm	< 2440 ppm
Non-linearity over the whole measuring range		E_Lin	< 330 ppm_FSV	< 1120 ppm_FSV	< 2240 ppm_FSV	< 4480 ppm_FSV
Repeatability (at 23°C)		E_Rep	< 50 ppm_FSV	< 240 ppm_FSV	< 480 ppm_FSV	< 960 ppm_FSV
Common-mode rejection ratio (without filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾			tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.		Tc_Gain	< 26 ppm/K	< 50 ppm/K	< 100 ppm/K	< 200 ppm/K
Temperature coefficient, typ.		Tc_Offset	< 120 ppm_FSV/K < 3.84 µV/V/K	< 460 ppm_FSV/K < 3.68 µV/V/K	< 920 ppm_FSV/K < 3.68 µV/V/K	< 1840 ppm_FSV/K < 3.68 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		No usage of this input in this mode
	Differential		tbd.	tbd.	tbd.	tbd.
	CommonMode		tbd.	tbd.	tbd.	tbd.

Noise (with/ without filtering)/ preliminary data:

Measurement mode		StrainGauge/SG 1/4-bridge 1 kΩ 2/3-wire
		32 mV/V	8 mV/V	4 mV/V (comp.) ⁵⁾	2 mV/V (comp.) ⁵⁾
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 350.0 ppm_FSV < 2734 digits < 11.2 µV/V	< 820.0 ppm_FSV < 6406 digits < 6.56 µV/V	< 1640.0 ppm_FSV < 12813 digits < 6.56 µV/V	< 3280.0 ppm_FSV < 25625 digits < 6.56 µV/V
	E_{Noise, RMS}	< 70.0 ppm_FSV < 547 digits < 2.24 µV/V	< 140.0 ppm_FSV < 1094 digits < 1.12 µV/V	< 280.0 ppm_FSV < 2188 digits < 1.12 µV/V	< 560.0 ppm_FSV < 4375 digits < 1.12 µV/V
	Max. SNR	> 83.1 dB	> 77.1 dB	> 71.1 dB	> 65.0 dB
	Noisedensity@1kHz	< 0.03	< 0.02	< 0.02	< 0.02
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< 85.0 ppm_FSV < 664 digits < 2.72 µV/V	< 48.0 ppm_FSV < 375 digits < 0.38 µV/V	< 96.0 ppm_FSV < 750 digits < 0.38 µV/V	< 192.0 ppm_FSV < 1500 digits < 0.38 µV/V
	E_{Noise, RMS}	< 14.0 ppm_FSV < 109 digits < 0.45 µV/V	< 8.0 ppm_FSV < 63 digits < 0.06 µV/V	< 16.0 ppm_FSV < 125 digits < 0.06 µV/V	< 32.0 ppm_FSV < 250 digits < 0.06 µV/V
	Max. SNR	> 97.1 dB	> 101.9 dB	> 95.9 dB	> 89.9 dB

²) In real bridge measurement, an offset adjustment is usually carried out after installation. The given offset specification of the box module 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 Features of the box module 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.

Note

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