Microchip Technology PT100 RTD, Руководство пользователя

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Installation and Operation
©
2006 Microchip Technology Inc. DS51607A-page 11
2.4.1.2 RTD SIGNAL CHAIN
The PGA is used to amplify the small voltage across the RTD. The reference input pin
of the PGA is connected to the RTD negative terminal and Channel 0 and Channel 1
are connected to the positive terminals of each RTD. This allows only the voltage
across the sensor to be amplified. The PGA has a gain error of ±1% (max.) for gains
greater than 1 V/V. Refer to the datasheet (DS21685) for details.
The RTD negative terminal and the PGA output are connected to the differential
amplifier. The differential amplifier scales the PGA output. The difference amplifier gain
is shown in Equation 2-1.
EQUATION 2-1: DIFFERENCE AMPLIFIER GAIN
2.4.1.3 THE GUI
The GUI uses a Microsoft Excel-based macro to open the USB port and communicate
with the PIC18F2550. When the file is opened, the macro checks hardware status. The
status display indicates hardware status as shown in Figure 2-6.
FIGURE 2-6: Hardware Status
When start is clicked, the macro double checks hardware availability before starting
the acquisition.
All user options such as
Sampling time, Stripchart buffer size , Digi. Pot Positions ,
or PGA Chn/Gain setup can be changed during acquisition.
G 1
2 R
F
×
R
G
20
Ω
+
-------------------------
⎝ ⎠
⎛ ⎞
+ =
Where:
R
F
= 10 k
Ω
R
G
= 10 k
Ω
Digital Potentiometer