Measurement SG 1/1 bridge (full bridge) 4/6-wire connection

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 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 ⋅ Tc_Cu) + R_-uv(1 + ∆T ⋅ Tc_Cu) )/R_nom with Tc_Cu~3930 ppm/K, R_nom

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.

Full bridge calculation:

Measurement SG 1/1 bridge (full bridge) 4/6-wire connection 1:

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

Measurement SG 1/1 bridge (full bridge) 4/6-wire connection 2:

Common data

Measurement mode	StrainGauge/SG/1/1 bridge 4/6 wire
Measurement mode	32 mV	4 mV		2 mV
Integrated power supply	1…5V adjustable, max. supply/Excitation 21 mA (internal electronic overload protection) therefore 120R DMS: up to 2.5 V; 350R DMS: up to 5.0 V
Measuring range, nominal	-32 … +32 mV/V		-4 … +4 mV/V		-2 … +2 mV/V
Measuring range, end value (FSV)	32 mV/V		4 mV/V		2 mV/V
Measuring range, technically usable	-34.359 … +34.359 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

Measurement mode		Measuring bridge/StrainGauge SG 1/1-Bridge 4/6-wire
Measurement mode		32 mV/V	4 mV/V	2 mV/V
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.003 %_FSV < ±30 ppm_FSV < ±0.96 µV/V	< ±0.0085 %_FSV < ±85 ppm_FSV < ±0.34 µV/V	< ±0.013 %_FSV < ±130 ppm_FSV < ±0.26 µV/V
	incl. Offset	< ±0.0075 %_FSV < ±75 ppm_FSV < ±2.4 µV/V	< ±0.03 %_FSV < ±300 ppm_FSV < ±1.2 µV/V	< ±0.06 %_FSV < ±600 ppm_FSV < ±1.2 µV/V
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. ²⁾ ⁶⁾	without Offset	< ±0.011 %_FSV < ±110 ppm_FSV < ±3.52 µV/V	< ±0.0515 %_FSV < ±515 ppm_FSV < ±2.06 µV/V	< ±0.099 %_FSV < ±990 ppm_FSV < ±1.98 µV/V
	incl. Offset	< ±0.013 %_FSV < ±130 ppm_FSV < ±4.16 µV/V	< ±0.059 %_FSV < ±590 ppm_FSV < ±2.36 µV/V	< ±0.115 %_FSV < ±1150 ppm_FSV < ±2.3 µV/V
Offset/Zero point deviation (at 23°C)	E_Offset	< 70 ppm_FSV	< 280 ppm_FSV	< 580 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 24 ppm	< 70 ppm	< 110 ppm
Non-linearity over the whole measuring range	E_Lin	< 18 ppm_FSV	< 45 ppm_FSV	< 65 ppm_FSV
Repeatability, over 24 h, with averaging	E_Rep	< 5 ppm_FSV	< 15 ppm_FSV	< 25 ppm_FSV
Common-mode rejection ratio (without filter) ³⁾	DC	tbd.	tbd.	tbd.
	50 Hz	tbd.	tbd.	tbd.
	1 kHz	tbd.	tbd.	tbd.
Common-mode rejection ratio (with 50 Hz FIR filter) ³⁾	DC	tbd.	tbd.	tbd.
	50 Hz	tbd.	tbd.	tbd.
	1 kHz	tbd.	tbd.	tbd.
Temperature coefficient, typ.	Tc_Gain	< 2.5 ppm/K	< 5 ppm/K	< 6 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 2 ppm_FSV/K < 0.06 µV/V/K	< 15 ppm_FSV/K < 0.06 µV/V/K	< 30 ppm_FSV/K < 0.06 µV/V/K
Largest short-term deviation during a specified electrical interference test		tbd.	tbd.	tbd.
Input impedance ±Input 1	Differential	tbd.	tbd.	tbd.
Input impedance ±Input 1	CommonMode	tbd.	tbd.	tbd.
Input impedance ±Input 2	4-wire	No usage of this input in this mode
	Differential	tbd.	tbd.	tbd.
	CommonMode	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.

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.

Measurement mode		Measuring bridge/StrainGauge SG 1/1-Bridge 4/6-wire
Measurement mode		32 mV/V	4 mV/V	2 mV/V
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 90 ppm_FSV < 703 digits < 2.88 µV/V	< 600 ppm_FSV < 4688 digits < 2.40 µV/V	< 1200 ppm_FSV < 9375 digits < 2.40 µV/V
	E_{Noise, RMS}	< 15 ppm_FSV < 117 digits < 0.48 µV/V	< 100 ppm_FSV < 781 digits < 0.40 µV/V	< 200 ppm_FSV < 1563 digits < 0.40 µV/V
	Max. SNR	> 96.5 dB	> 80.0 dB	> 74.0 dB
	Noisedensity@1kHz	< 6.79	< 5.66	< 5.66
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< 12 ppm_FSV < 94 digits < 0.38 µV/V	< 60 ppm_FSV < 469 digits < 0.24 µV/V	< 120 ppm_FSV < 938 digits < 0.24 µV/V
	E_{Noise, RMS}	< 2.0 ppm_FSV < 16 digits < 0.06 µV/V	< 10.0 ppm_FSV < 78 digits < 0.04 µV/V	< 20.0 ppm_FSV < 156 digits < 0.04 µV/V
	Max. SNR	> 114.0 dB	> 100.0 dB	> 94.0 dB

Measurement SG 1/1 bridge (full bridge) 4/6-wire connection

Common data

Specific data ELM3702-0101