6.4.5 IPTS-68 Conversion
The IPTS-68 characterization convertsresistance to temperature according to
the InternationalPractical Temperature Scale of 1968. The applicable coeffi-
cients are R0(“r0”), α(“ALPHA”), δ(“dELtA”),a4(“A4”), and c4(“C4”).
Youcan also select the temperature scale (“SCALE”) as IPTS-68 (“68”) or
ITS-90 (“90”). Selecting ITS-90 causes the temperatureto be adjusted by a
smallamount equal to the difference between the ITS-90 and IPTS-68 tempera-
ture scales.
6.4.5.1 Setting the Characterization Coefficients
Probe characterization coefficients are setw ithin the Probemenu after select-
ing the probe characterization type. Each coefficientappears with its name
shownb riefly followedby its value. For example,
A4+4.336079
Forsome coefficients, you only need to set the digits in the number. Other coef-
ficientsalso have a sign as shown above (positive sign appears as “+”). Use the
Land Rbuttonsto move between digits (and the sign). The selected digit
willflash. Use the Uand Dbuttons to ch ange a digit. Once the sign and digits
are correct, press Enter to accept the number.If you decide you would like to
cancel anychanges you have made, you may do so by pressing the Ω/Exit but-
ton. Thiswill immediately skip to the next coefficient.
If the coefficientalso requires an exponent, it will appear after setting the num-
ber as follows:
E -04
Increase or decrease the exponentusing the p and q buttons. Once the exponent
is correct press Enter to accept it.
6.4.5.2 Testing the Coefficients
The 1502A 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 theLand Rbuttons to move between digits and the Uand Dbuttons
to change a digit. After setting the resistance press Enter.The 1502A will cal-
culateand display the temperature corresponding to the resistance you entered.
21
6 General Operation
Selecting the Probe Characterization