Measurement Sg 1/1 Bridge (Full Bridge) 4/6-Wire Connection - Beckhoff EPP3504-0023 Short Manual

3.2.6

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

Some notes to EPP3504-0023 full bridge measurement:
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 (1 + ∆T ⋅ Tc ) + R
+uv Cu -uv
e.g. 350 Ω and R or R
+uv
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.
Note: specifications apply for 5 V SG excitation and symmetric 350R SG.
Note: data are valid from production week 01/ 2019 and
• for EPP3504-0023: HW04
Full bridge calculation:
EPP3504-0023
(1 + ∆T ⋅ Tc ) )/R with Tc
Cu nom
lead resistances respectively.
-uv
~3930 ppm/K, R
Cu nom
Version: 1.2
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