Application Note

4 Fluke Corporation Measuring uncommon RTDs with the Fluke 726
Sending custom RTD constants to the
Fluke 726
Once communication is established you can load
custom constants into the 726. You can also send
queries to the 726 to check the current settings and
to verify your changes. Here is an overview of the
steps to modify the constants:
1. Set the RTD type to the one of the custom types
(CUST1, CUST2 or CUST3)
2. Set the minimum and maximum temperatures for
the custom RTD
3. Set the constants R0, A, B, and C
4. Assign a six-character name that will appear
on the front panel of the instrument to help the
operator choose RTD types
The best way to show the detailed process is
through an example. Let’s say we need to measure
an RTD with the following attributes:
Range is from 0 to 630 °C
R
0
= 100 W
A = 3.9692 x 10
-3
B = -5.8495 x 10
-7
C = unknown and unnecessary since range is
0 °C or greater
Rather than having to type all of the commands
each time we want to change the constants, we
can define short text files and send them using
the HyperTerminal program. The Windows Note-
pad program may be used to create and edit the
command scripts.
The text file in Figure 6 is designed to query all
of the parameters associated with the RTD type
CUST1. Try building and sending this query file first.
It is a good practice script and is useful for verifying
any changes you make to the constants later.
When you finish editing the script file, make sure
you hit Enter after the last command (in this exam-
ple “cust1_alias?”). The cursor should be blinking
below the last command when you save the file.
This will ensure that the 726 sees the endline after
the last command and processes it.
To send a script file to the 726, click on Transfer,
Send Text File in HyperTerminal. The 726 will
respond to each of the queries with the current
values of each constant.
Figure 6. A script used to query custom RTD settings and the results
of sending it to the 726. Each query command is followed by a
response from the 726.
The HyperTerminal window shown in Figure
6 shows the response of the 726 to sending the
query commands. Each command that ends in a
question mark is followed by a response from the
726. These response are the factory default values
for the CUST1 RTD.