Measurement-computing CIO-EXP-RTD16 Instrukcja Użytkownika Pobierz pdf (Strona 20)

5.6.1 Two-wire RTD Hookup

+IEXC (EXCITATION CURRENT (+))

+ SENSE

- SENSE

?????

CAO

-IEXC (EXCITATION CURRENT

(−))

2-WIRE

RTD

Add Jumper Wires

Between Terminals

CIO-EXP-RTD BOARD

A two wire RTD has two leads, one to each side

of the temperature sensitive resistor. The

excitation current is connected directly to the

leads at the CIO-EXP-RTD16 screw terminals. A

two wire connection is less accurate than the 4

wire type, and so is not the first choice for the

best measurements. The reason for the inaccuracy

is that there is a varying resistance associated with

the excitation current flowing in the sense leads

and this resistance is added to the measurement.

The amount of inaccuracy is determined by the

wire

e and len

th.

Figure 5-4. Two-Wire RTD Connections

5.6.2 Three-Wire RTD Hookup

+IEXC (EXCITATION CURRENT (+))

+ SENSE

SENSE

?????

CAO

-IEXC (EXCITATION CURRENT

(

−

))

3-WIRE

RTD

CIO-EXP-RTD BOARD

NOTE: The CIO-EXP-RTD uses a non-standard 3-wire hook-up.

A three-wire RTD connection allows the use of

special circuit to compensate for resistance

variations in the lead wires with temperature

changes (Figure 5-5 at right).

NOTE: The +Sense terminal is not used in this

non-standard hookup.

Figure 5-5. Three-Wire RTD Connections

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 26

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