United Electronic Industries DNA-AI-208, Руководство пользователя

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DNx-AI-208 Analog Input Layer
25
Tel: 508-921-4600 www.ueidaq.com Vers: 4.6
Date: November 2013 File: AI-208 App B.fm
© Copyright 2009
United Electronic Industries, Inc.
Simulating a load is usually done by adding a larger resistance in parallel with
one of the branches. To simulate a compression load
, we need to add a shunt
resistance to Rg and to simulate a tension load , we need to add a resistance to
R3.
The following figure assumes that all branch resistances are equal to Rg (strain
gauge resistance) and that the R4 branch was shunted with a resistance Rs
(shunt resistance).
Figure B-2. Strain Gauge with Shunt Resistance R
s
Added
Δ
Vout Vex
R4
R4 Rs +
--------------------
R3
R4
R4 Rs +
-------------------- +
----------------------------------
R4
R3 R4 +
--------------------- –
 
 
 
 
 
=
Eq. 3:
Δ
Vout -Vex
Rg
4Rs 2Rg +
---------------------------
 
 
=
Eq. 4:
After replacing R4 with (R4.Rs)/(R4+Rs) in Equation 1, the voltage output of the
bridge when the shunt calibration resistor is enabled is:
The voltage output change after enabling the shunt resistor is
Δ
Vout = Vouts – Vout .
In most applications, all branches of the Wheatstone bridge use the same resis-
tance. Standard values for Rg are 120, 350, and 1000 Ohms. After setting R1=
R2= R3=Rg, Equation 3 becomes:
Vex
Vout
S+
S-
R1
R2
R3
R4(Rg)
Rs
Vout Vex
R4
R4 Rs +
--------------------
R3
R4
R4 Rs +
-------------------- +
----------------------------------
R1
R1 R2 +
--------------------- –
 
 
 
 
 
=
Eq. 2: