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 box module 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 box module.

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 box module 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.

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.

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:

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 120R SG: up to 2.5 V; 350R SG: up to 5.0 V
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

Preliminary specifications:

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⁾
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.005 %_FSV < ±50 ppm_FSV < ±1.6 µV/V	< ±0.012 %_FSV < ±120 ppm_FSV < ±0.96 µV/V	< ±0.017 %_FSV < ±170 ppm_FSV < ±0.68 µV/V	< ±0.026 %_FSV < ±260 ppm_FSV < ±0.52 µV/V	< ±0.024 %_FSV < ±240 ppm_FSV < ±0.96 µV/V	< ±0.048 %_FSV < ±480 ppm_FSV < ±0.96 µV/V
	incl. Offset	< ±0.015 %_FSV < ±150 ppm_FSV < ±4.8 µV/V	< ±0.03 %_FSV < ±300 ppm_FSV < ±2.4 µV/V	< ±0.06 %_FSV < ±600 ppm_FSV < ±2.4 µV/V	< ±0.12 %_FSV < ±1200 ppm_FSV < ±2.4 µV/V	< ±0.06 %_FSV < ±600 ppm_FSV < ±2.4 µV/V	< ±0.12 %_FSV < ±1200 ppm_FSV < ±2.4 µV/V
Offset/Zero point deviation (at 23°C)	E_Offset	< 140 ppm_FSV	< 280 ppm_FSV	< 560 ppm_FSV	< 1160 ppm_FSV	< 560 ppm_FSV	< 1120 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 40 ppm	< 100 ppm	< 140 ppm	< 220 ppm	< 200 ppm	< 400 ppm
Non-linearity over the whole measuring range	E_Lin	< 30 ppm_FSV	< 60 ppm_FSV	< 90 ppm_FSV	< 130 ppm_FSV	< 120 ppm_FSV	< 240 ppm_FSV
Repeatability	E_Rep	< 10 ppm_FSV	< 20 ppm_FSV	< 30 ppm_FSV	< 40 ppm_FSV	< 40 ppm_FSV	< 80 ppm_FSV
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.	Tc_Gain	< 2 ppm/K	< 4 ppm/K	< 6 ppm/K	< 10 ppm/K	< 8 ppm/K	< 16 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 2.4 ppm_FSV/K < 0.08	< 10 ppm_FSV/K < 0.08	< 24 ppm_FSV/K < 0.1	< 50 ppm_FSV/K < 0.1	< 20 ppm_FSV/K < 0.08	< 40 ppm_FSV/K < 0.08
Largest short-term deviation during a specified electrical interference test		0.03 %_FSV = 300 ppm_FSV typ.	0.06 %_FSV = 600 ppm_FSV typ.	0.12 %_FSV = 1200 ppm_FSV typ.	0.24 %_FSV = 2400 ppm_FSV typ.	0.12 %_FSV = 1200 ppm_FSV typ.	0.24 %_FSV = 2400 ppm_FSV typ.
Input impedance ±Input 1	Differential	tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1	Common- Mode	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.
	Common- Mode	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 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 Features 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.

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.

Noise (with/ without filtering):

Measurement mode		Measuring bridge/StrainGauge SG 1/1-Bridge 4/6-wire
		32 mV/V	8 mV/V	4 mV/V	2 mV/V
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 85.0 ppm_FSV < 664 digits < 2.72 µV/V	< 300.0 ppm_FSV < 2344 digits < 2.4 µV/V	< 600.0 ppm_FSV < 4688 digits < 2.4 µV/V	< 1200.0 ppm_FSV < 9375 digits < 2.4 µV/V
	E_{Noise, RMS}	< 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
	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 filter, at 23°C)	E_{Noise, PtP}	< 12.0 ppm_FSV < 94 digits < 0.38 µV/V	< 30.0 ppm_FSV < 234 digits < 0.24 µV/V	< 60.0 ppm_FSV < 469 digits < 0.24 µV/V	< 120.0 ppm_FSV < 938 digits < 0.24 µV/V
	E_{Noise, RMS}	< 2.0 ppm_FSV < 16 digits < 0.06 µV/V	< 5.0 ppm_FSV < 39 digits < 0.04 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	> 106.0 dB	> 100.0 dB	> 94.0 dB