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 terminal 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 terminal.

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 terminal 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 terminal. 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		Measuring bridge/StrainGauge SG 1/2-Bridge 5/3-wire
		16 mV/V	8 mV/V ¹⁾	4 mV/V ¹⁾	2 mV/V ¹⁾	4 mV/V (comp.) ^{1) 5)}	2 mV/V (comp.) ^{1) 5)}
Integrated power supply		1…5V adjustable, max. power 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
Basic accuracy: Measuring deviation at 23°C, with averaging, typ. ²⁾	without Offset	< ±0.011 %_FSV < ±110 ppm_FSV < ±1.76 µV/V	< ±0.022 %_FSV < ±220 ppm_FSV < ±1.76 µV/V	< ±0.044 %_FSV < ±440 ppm_FSV < ±1.76 µV/V	< ±0.0925 %_FSV < ±925 ppm_FSV < ±1.85 µV/V	< ±0.044 %_FSV < ±440 ppm_FSV < ±1.76 µV/V	< ±0.088 %_FSV < ±880 ppm_FSV < ±1.76 µV/V
	incl. Offset	< ±0.04 %_FSV < ±400 ppm_FSV < ±6.40 µV/V	< ±0.075 %_FSV < ±750 ppm_FSV < ±6 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 µV/V	< ±0.3 %_FSV < ±3000 ppm_FSV < ±6 µV/V
Extended basic accuracy: Measuring deviation at 0…55°C, with averaging, typ. ^{2) 6)}	without Offset	< ±0.052 %_FSV < ±520 ppm_FSV < ±8.32 µV/V	< ±0.087 %_FSV < ±870 ppm_FSV < ±6.96 µV/V	< ±0.1585 %_FSV < ±1585 ppm_FSV < ±6.34 µV/V	< ±0.313 %_FSV < ±3130 ppm_FSV < ±6.26 µV/V	< ±0.174 %_FSV < ±1740 ppm_FSV < ±6.96 µV/V	< ±0.3475 %_FSV < ±3475 ppm_FSV < ±6.95 µV/V
	incl. Offset	< ±0.0645 %_FSV < ±645 ppm_FSV < ±10.32 µV/V	< ±0.113 %_FSV < ±1130 ppm_FSV < ±9.04 µV/V	< ±0.2065 %_FSV < ±2065 ppm_FSV < ±8.26 µV/V	< ±0.403 %_FSV < ±4030 ppm_FSV < ±8.06 µV/V	< ±0.2255 %_FSV < ±2255 ppm_FSV < ±9.02 µV/V	< ±0.4505 %_FSV < ±4505 ppm_FSV < ±9.01 µV/V
Offset/Zero point deviation (at 23°C)	E_Offset	< 385 ppm_FSV	< 715 ppm_FSV	< 1325 ppm_FSV	< 2530 ppm_FSV	< 1430 ppm_FSV	< 2860 ppm_FSV
Gain/scale/amplification deviation (at 23°C)	E_Gain	< 70 ppm	< 130 ppm	< 260 ppm	< 510 ppm	< 260 ppm	< 520 ppm
Non-linearity over the whole measuring range	E_Lin	< 85 ppm_FSV	< 175 ppm_FSV	< 350 ppm_FSV	< 760 ppm_FSV	< 350 ppm_FSV	< 700 ppm_FSV
Repeatability, over 24 h, with averaging	E_Rep	< 12 ppm_FSV	< 25 ppm_FSV	< 50 ppm_FSV	< 120 ppm_FSV	< 50 ppm_FSV	< 100 ppm_FSV
Temperature coefficient, typ.	Tc_Gain	< 5 ppm/K	< 8 ppm/K	< 15 ppm/K	< 25 ppm/K	< 16 ppm/K	< 32 ppm/K
Temperature coefficient, typ.	Tc_Offset	< 15 ppm_FSV/K < 0.24 µV/V/K	< 25 ppm_FSV/K < 0.20 µV/V/K	< 45 ppm_FSV/K < 0.18 µV/V/K	< 90 ppm_FSV/K < 0.18 µV/V/K	< 50 ppm_FSV/K < 0.20 µV/V/K	< 100 ppm_FSV/K < 0.20 µV/V/K
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.
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.

¹) Adjustment of the half-bridge measurement and thus validity of the data from production week 2018/50 and for ELM3502: HW03/ for ELM3504: HW04

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.

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.

ELM3502 (20 ksps)

Measurement mode		StrainGauge/SG 1/2 Bridge 3/5 wire
		16 mV/V	8 mV/V	4 mV/V	2 mV/V
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 600 ppm_FSV < 4688 digits < 9.60 µV/V	< 1200 ppm_FSV < 9375 digits < 9.60 µV/V	< 2400 ppm_FSV < 18750 digits < 9.60 µV/V	< 4800 ppm_FSV < 37500 digits < 9.60 µV/V
	E_{Noise, RMS}	< 100 ppm_FSV < 781 digits < 1.60 µV/V	< 200 ppm_FSV < 1563 digits < 1.60 µV/V	< 400 ppm_FSV < 3125 digits < 1.60 µV/V	< 800 ppm_FSV < 6250 digits < 1.60 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 filtering, at 23°C)	E_{Noise, PtP}	< 35 ppm_FSV < 273 digits < 0.56 µV/V	< 70 ppm_FSV < 547 digits < 0.56 µV/V	< 140 ppm_FSV < 1094 digits < 0.56 µV/V	< 280 ppm_FSV < 2188 digits < 0.56 µV/V
	E_{Noise, RMS}	< 6.0 ppm_FSV < 47 digits < 0.10 µV/V	< 12.0 ppm_FSV < 94 digits < 0.10 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

ELM3504 (10 ksps)

Measurement mode		StrainGauge/SG 1/2 Bridge 3/5 wire
		16 mV/V	8 mV/V	4 mV/V	2 mV/V
Noise (without filtering, at 23°C)	E_{Noise, PtP}	< 600 ppm_FSV < 4688 digits < 9.60 µV/V	< 1200 ppm_FSV < 9375 digits < 9.60 µV/V	< 2400 ppm_FSV < 18750 digits < 9.60 µV/V	< 4800 ppm_FSV < 37500 digits < 9.60 µV/V
	E_{Noise, RMS}	< 100 ppm_FSV < 781 digits < 1.60 µV/V	< 200 ppm_FSV < 1563 digits < 1.60 µV/V	< 400 ppm_FSV < 3125 digits < 1.60 µV/V	< 800 ppm_FSV < 6250 digits < 1.60 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 filtering, at 23°C)	E_{Noise, PtP}	< 35 ppm_FSV < 273 digits < 0.56 µV/V	< 70 ppm_FSV < 547 digits < 0.56 µV/V	< 140 ppm_FSV < 1094 digits < 0.56 µV/V	< 280 ppm_FSV < 2188 digits < 0.56 µV/V
	E_{Noise, RMS}	< 6.0 ppm_FSV < 47 digits < 0.10 µV/V	< 12.0 ppm_FSV < 94 digits < 0.10 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 terminal 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 terminal itself or the control/PLC on application side or the abstract offset error have to be entered into the balancing parameter S0 of the terminal. 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.