[]
()()
()[]rtC 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,andβcoefficientsusing
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 providesa convenient method for testing the coefficients you have
entered tomake sure they have been entered correctly. This is done by calculat-
ing temperature for givenresistances and comparing the results with tempera-
tures listed on the probe’scalibration repo rt. This conversiontest function is
located at theend of the Probe menu. After setting the coefficients“tESt”ap
-
pears briefly followedby the resistance value. You can change the resistance by
using theUand Dbuttons to move between digits and the Land Rbuttons
to change a digit. After setting the resistance press Enter.The 1504 will calcu-
lateand display the temperature corresponding to the resistance you entered.
Compare this temperature with the temperatures listed on the probe calibration
report toverify that the coefficients you entered are correct.
6.5 Filtering
Whilemeasuring temperature, the readings may appear to vary. This may be
due to actualvariations in temperature or electrical noise internal to the 1504.
The filterhelp s to smooth variationsin the measur ements and improveresolu-
tion. The drawbackis that filtering tends to slow the response to changes in
temperature. Youcan increase the filter time constant to further improve accu-
racyand resolution or decrease the time constant to reduce the response time.
Youcan set it to any value between 0 and 60 seconds. A value of 0 disables the
filter.The default time constant is 4 seconds.
Tochange 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
filtervalue. Use the Uand Dbuttons to in crease or decrease the filter value
then press Enter.The next parameter in the menu, the current, will then appear.
6.6 Power Saver
The powersaver 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
powersaver 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