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7.6.5.1
Set External
When using an external reference resistor, you must specify its resistance using
this SET EXT soft-key. Access to the SET EXT function may be locked out as
explained in Section 7.6.5.4.
NOTE:
When using an external reference resistor, you must enter the pre-
cise value of the resistance with the SET EXT function for the driving cur-
rent and the measured resistance to be accurate.
The following steps explain how to setup an external reference resistor:
1.
Connect the reference resistor to Input 2 on the 1575/1590. It is impor-
tant to use the proper reference resistor for the probe being used. For
lowest noise, a 100 ohm resistor should be used with 25 ohm and 100
ohm SPRTs (see Table 5, Reference Resistor Selection, for more
information).
2.
The external reference needs to be properly configured in order to obtain
proper measurements and driving current. To set the value of the refer-
ence resistor use System Menu|System Cal|Set Ext and enter the resis-
tance of the external resistor attached to Input 2 and press "Enter".
Example: If your reference resistor is 99.99985 ohms, enter 99.99985
into the "External" field.
3.
Use Probe Menu|Select Channel|Input 2 to see which probe is assigned
to Input 2. Firmware will not allow you to use a probe with an external
reference if it is assigned to Input 2. If a probes is assigned to Input 2
and attempted to be used with an external reference, the error "INPUT 2
CANNOT USE EXTERNAL REFERENCE! PLEASE WAIT . . ." will
appear when trying to set the probe reference to external.
4.
If the probe to be used with an external reference is assigned to Input 2,
use the following instructions to remedy the problem:
•
Use Probe Menu|Select Channel and select Input 2
•
Next use Probe Menu|Select Probe and select a probe number that is not
used or a probe number that will not be used with an external reference.
5.
To set up a probe to use an external reference, use Probe Menu|Edit
Probe and set the Reference parameter to "External" (see Section 8.4.3
for more details).
6.
If an error is given while trying to set up a probe to use external, use
steps 3 through 5 to verify that all settings have been properly set and ap-
plied. NOTE: "Enter" has to be pressed to apply any changes made to
any field.
1575/1590 Thermometer Readout
User’s Guide
94