SCP SCIENCE DigiPREP - Possible A;D Problem; RTD Input Connection

KeyPad
Version 1.0
SCP SCIENCE
31
POSSIBLE A/D PROBLEM
If the DigiPROBE is reading the
wrong temperature, make sure that
the DigiPROBE itself is functional
before looking at the converter
circuit. This can be accomplished by
measuring the resistance across pin
1 and 2 of the DigiPROBE connec-
tor.
Typical 25oC = 108 ohms.
RTD INPUT CONNECTION
• Visually inspect the external connection of the
DigiPROBE.
• Unscrew the bottom plate by removing the 4
screws that are holding the feet in place. Make
sure that the J9 connector is fullt connected with
the header (see fi gure 21 for location). If it is, then
start investigating the circuit as explained below.
A/D POWER AND CONNECTIONS
• Disconnect J9 from the board, then power up the
controller. With the negative lead of a multimeter
on TP6 and its positive lead on the test points
below (see fi gure 22), you should read the
following measurements:
ANALOG CIRCUIT MEASUREMENTS
WITH J9 OPEN
Test Point Required Value
TP7 5V
TP11 5V
TP10 1V
TP12 0V
• Now on J9, short pins 2 and 3, short pins 4 and 5
and insert a 200 ohms 1% precision resistor
between pins 3 and 4, you should read the
following measurements:
ANALOG CIRCUIT MEASUREMENTS WITH
100 OHMS RESISTOR BETWEEN PINS 3
AND 4 OF J9
Test Point Required Value
TP7 5V
TP11 5V
TP10 1V
TP14 1.95V
TP13 0.95V
TP12 2.60V
If you fail to get those values, the analog section is
faulty; the KeyPad PCB must be replaced.
FIGURE 21: J9 CONNECTOR LOCATION
Legend
1. J9 header with RTD cable connection
NOTE