Measurement SG 1/2 bridge (half bridge) 3/5-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 ±16 mV/V ⋅ 5 V = ±80 mV; the internal circuits are designed for the 160 mV of the full bridge measurement.

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 5 wire connection. External line resistances are compensated by the 5 wire connection and the half bridge is detected directly from the measuring channel.
In the 3 wire connection, the box module generally has the same specification, but its view of the connected half bridge is clouded by the unclear and temperature-dependent lead resistances within cables and connectors. In this respect, the overall system "half 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 5 wire connection is recommended.

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 3.5 V SG excitation and symmetric 350R SG.

To calculate the R_1/2 half bridge:

Measurement SG 1/2 bridge (half bridge) 3/5-wire connection 1:

R_3/4 are the internal switchable supplementary resistors of the box module. They have a high resistance of a few kΩ compared to R_1/2 and thus do not significantly load the internal supply.

Other half-bridge configurations (e.g. R_1/4 or R_1/3 variable) cannot be connected.

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

Measurement SG 1/2 bridge (half bridge) 3/5-wire connection 2:

N should be chosen based on the mechanical configuration of the variable resistors (Poisson, 2 active uniaxial, …). The channel value (PDO) is interpreted directly [mV/V].

Measurement mode	StrainGauge/SG 1/2-Bridge 5/3-wire
	16 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	-16 … 16 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)	16 mV/V	8 mV/V	4 mV/V	2 mV/V	4 mV/V	2 mV/V
Measuring range, technically usable	-17.179 … 17.179 mV/V	-8.589 … 8.589 mV/V	-4.294 … 4.294 mV/V	-2.147 … 2.147 mV/V	-4.294 … 4.294 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		StrainGauge/SG 1/2-Bridge 5/3-wire
		16 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	< ±0.022%_FSV < ±220 ppm_FSV < ±3.52 µV/V	< ±0.044%_FSV < ±440 ppm_FSV < ±3.52 µV/V	< ±0.088%_FSV < ±880 ppm_FSV < ±3.52 µV/V	< ±0.185%_FSV < ±1850 ppm_FSV < ±3.7 µV/V	< ±0.088%_FSV < ±880 ppm_FSV < ±3.52 µV/V	< ±0.176%_FSV < ±1760 ppm_FSV < ±3.52 µV/V
	with Offset	< ±0.08%_FSV < ±800 ppm_FSV < ±12.8 µV/V	< ±0.075%_FSV < ±750 ppm_FSV < ±6.00 µV/V	< ±0.14%_FSV < ±1400 ppm_FSV < ±5.60 µV/V	< ±0.27%_FSV < ±2700 ppm_FSV < ±5.40 µV/V	< ±0.15%_FSV < ±1500 ppm_FSV < ±6.00 µV/V	< ±0.30%_FSV < ±3000 ppm_FSV < ±6.00 µV/V
Offset/Zero point deviation (at 23°C)	E_Offset	< 770 ppm_FSV	< 1430 ppm_FSV	< 2650 ppm_FSV	< 5060 ppm_FSV	< 2860 ppm_FSV	< 5720 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 140 ppm	< 260 ppm	< 520 ppm	< 1020 ppm	< 520 ppm	< 1040 ppm
Non-linearity over the whole measuring range	E_Lin	< 170 ppm_FSV	< 350 ppm_FSV	< 700 ppm_FSV	< 1520 ppm_FSV	< 700 ppm_FSV	< 1400 ppm_FSV
Repeatability	E_Rep	< 24 ppm_FSV	< 50 ppm_FSV	< 100 ppm_FSV	< 240 ppm_FSV	< 100 ppm_FSV	< 200 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	DC: tbd.	DC: tbd.	DC: tbd.	DC: tbd.	DC: tbd.	DC: tbd.
	50 Hz	tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
	1 kHz	tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
Temperature coefficient, typ.	Tc_Gain	< 10 ppm/K	< 16 ppm/K	< 30 ppm/K	< 50 ppm/K	< 32 ppm/K	< 64 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 30 ppm_FSV/K < 0.48 µV/V/K	< 50 ppm_FSV/K < 0.4 µV/V/K	< 90 ppm_FSV/K < 0.36 µV/V/K	< 180 ppm_FSV/K < 0.36 µV/V/K	< 100 ppm_FSV/K < 0.4 µV/V/K	< 200 ppm_FSV/K < 0.4 µV/V/K
Largest short-term deviation during a specified electrical interference test		tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1 (internal resistance)	Differential	tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 1 (internal resistance)	CommonMode	tbd.	tbd.	tbd.	tbd.	tbd.	tbd.
Input impedance ±Input 2 (internal resistance)	3-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 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		StrainGauge/SG 1/2-Bridge 5/3-wire
		16 mV/V	8 mV/V	4 mV/V	2 mV/V
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 600.0 ppm_FSV < 4688 digits < 9.6 µV/V	< 1200.0 ppm_FSV < 9375 digits < 9.6 µV/V	< 2400.0 ppm_FSV < 18750 digits < 9.6 µV/V	< 4800.0 ppm_FSV < 37500 digits < 9.6 µV/V
	E_{Noise, RMS}	< 100.0 ppm_FSV < 781 digits < 1.6 µV/V	< 200.0 ppm_FSV < 1563 digits < 1.6 µV/V	< 400.0 ppm_FSV < 3125 digits < 1.6 µV/V	< 800.0 ppm_FSV < 6250 digits < 1.6 µV/V
	Max. SNR	> 80.0 dB	> 74.0 dB	> 68.0 dB	> 61.9 dB
	Noisedensity@1kHz	< 22.63	< 22.63	< 22.63	< 22.63
Noise (with 50 Hz FIR filter, at 23°C)	E_{Noise, PtP}	< 35.0 ppm_FSV < 273 digits < 0.56 µV/V	< 70.0 ppm_FSV < 547 digits < 0.56 µV/V	< 140.0 ppm_FSV < 1094 digits < 0.56 µV/V	< 280.0 ppm_FSV < 2188 digits < 0.56 µV/V
	E_{Noise, RMS}	< 6.0 ppm_FSV < 47 digits < 0.1 µV/V	< 12.0 ppm_FSV < 94 digits < 0.1 µV/V	< 22.0 ppm_FSV < 172 digits < 0.09 µV/V	< 45.0 ppm_FSV < 352 digits < 0.09 µV/V
	Max. SNR	> 104.4 dB	> 98.4 dB	> 93.2 dB	> 86.9 dB

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.

	Validity of property values The resistor of the bridge is positioned parallel to the internal resistor of the box module and leads to an offset shifting respectively. The Beckhoff factory calibration will be carried out with the half bridge 350 Ω, thus the values specified above are directly valid for the 350 Ω half bridge. By connection of another dimensioned half-bridge is to: perform a balancing (offset correction) by the box module itself or the control/PLC on application side or the abstract offset error have to be entered into the balancing parameter S0 of the box module. Example: a 350 Ω half bridge correlates by the compensated effect of the input resistor (2 MΩ) during factory calibration 0.26545 %_FSV (16 mV/V), that corresponds to 20738 digits.