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The
DB-889D have two 37-pin D-sub connector and two 20-pin header. the one
D-sub connector connected to A/D Board's analog input connector and another
one can be cascaded to another sceondery DB-889D.The 20-pin header is
DB-889D' control logic circute. It is connected to A/D board's digital
output port from 20-pin flat cable. then the digital output can control
multi-plexer and amplifer. |
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DB-889D
provides 16-channel analog input and CJC circuit for thermocouple input.
THERMO-COUPLE with CJC
we would like the A/D card to read only V1, but by connecting the DB-889D
in attempt to measure the output of junction J1, we have created two more
metallic junction: J2 and J3, since J3 is a copper to copper junction,
It creates no thermal EMF (V3=0) but J2 is a copper-to-constantan junction
which will add an EMF(V2) In oppositional to the temperature dif-frewnce
between J1 and J2. This says that we can't find the temperature at J1
unless we first find the temperature of J2.
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Example:
Input T-type thermo-couple; Setup DB-889D Gain: 500
- reading thermocouple voltage : Vt
- reading CJC volatge : Vcjc
- caculate Vcjc to temperature : Tcjc = Vc *1000 / 24.4
- change Tcjc to T-type thermocouple
Voltage : Vtv
- (refer. T-type thermocouple table T-to-V
)
- caculate Vt + Vtv =Vtc
- Change Vtc to temperature =
T
- (refer. T-type thermocouple table V-to-T)
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ICP DAS Co., Ltd. All Rights Reserved |
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