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[]
()
()
()
[]
rt C
RAtB
RAtBtCt t
t
t
°=
++
++ + −
≥
<
⎧
⎨
⎩
⎪
0
2
0
23
1
1 100
0
0
The A, B, and C coefficients can be converted to α, δ,andβ coefficients using
the following formulas:
αδ β=+ =−
+
=−
+
AB
A
B
C
AB
100
100
100
1
10
100
8
6.4.5 Testing the coefficients
The 1504 provides a convenient method for testing the coefficients you have
entered to make sure they have been entered correctly. This is done by calculat
-
ing temperature for given resistances and comparing the results with tempera
-
tures listed on the probe’s calibration report. This conversion test function is
located at the end of the Probe menu. After setting the coefficients “tESt”ap
-
pears briefly followed by the resistance value. You can change the resistance by
using the U and D buttons to move between digits and the L and R buttons
to change a digit. After setting the resistance press Enter. The 1504 will calcu-
late and display the temperature corresponding to the resistance you entered.
Compare this temperature with the temperatures listed on the probe calibration
report to verify that the coefficients you entered are correct.
6.5 Filtering
While measuring temperature, the readings may appear to vary. This may be
due to actual variations in temperature or electrical noise internal to the 1504.
The filter helps to smooth variations in the measurements and improve resolu
-
tion. The drawback is that filtering tends to slow the response to changes in
temperature. You can increase the filter time constant to further improve accu
-
racy and resolution or decrease the time constant to reduce the response time.
You can set it to any value between 0 and 60 seconds. A value of 0 disables the
filter. The default time constant is 4 seconds.
To change the filter value, enter the Sample menu. This is done by first press
-
ing the Menu button (“SEt?” appears) then pressing the F/Sample button.
The display will briefly indicate “SA Par”, then “FILtEr”, then the current
filter value. Use the U and D buttons to increase or decrease the filter value
then press Enter. The next parameter in the menu, the current, will then appear.
6.6 Power Saver
The power saver feature is useful for conserving power when operating from a
battery. It causes the display to blank after a period of no user activity. The
power saver feature can reduce operating current by as much as 100 mA. While
the display is blanked a small illuminated dot appears on the left side of the dis
-
1504 Thermometer Readout
User’s Guide
22