TemperatureLAB  Version 2.1

(c) 10/1999  James D. Purdy

 TemperatureLAB  is a library written for the HP-48 series
calculator to perform temperature measurement and calibration calculations  using
NTC thermistors and 100 Ohm Platinum RTD's.   It is based  on industry standard Hart-Stienhart
and second-order Callendar equations for conversion of temperature and resistance values.

There are two conversion programs, one for RTD's and one for thermistors, along with  common
supporting utilities.    TemperatureLAB is written in SysRPL and does not contain any machine-spacific calls,
so it will be compatible with most HP's.

• Convert between temperature and resistance for NTC (negative temperature coefficient) thermistors and RTD's.

The conversion is automatic  if units of ohms or Deg C are given.  The user may select  the direction of conversion
and omit the units; however, the conversion is always done  in the appropriate direction if units are specified.
 
• Produce calibration tables for each device give a start value, in ohms or degrees C,  and an increment value.

This function may be useful if multiple conversions are necessary or values close to a measurement point are desired.
The user may jump to a value or change the increment value while running this program.
 
•  Enter and/or edit the equation constants for each conversion program.  This allows the user

the flexibility to use instruments which are supplied with calibration constants.
 
• Curve fit calibration data given several known temperature resistance pairs.  These are supplied in the form of a matrix

and the required constants for the conversion equations are calculated and stored.
 

TemperatureLAB is supplied in two configurations.  The library TLAB has all of the
features listed above and is about 5k.   TLABlt  contains the convertor programs
but not the Temperature Table program TBL.  This library is about 3k.

There ia a data directory TLAB.DIR with two sub directories  DATA and CONS.   DATA contains
several data sets so that the curve fitting program may be examined.     CONS contains
constant files which correspond to ASTM standard thermistors and the ITS-90 standard RTD.

• Download the library into the HP using KERMIT or HP Explorer.
• Store the library in any port.
• Delete the downloaded library .
• Cycle the power to the calculator.
• More detailed installation instruction may be found here.  Installation

• Before the conversion programs will run correctly, constants must be entered.
• A default and set of constants is stored in the correct variables by running >TCON and >RCON as described below.
• The variables are stored in the current directory.

 THERM converts between temperature and resistance for NTC thermistors.
Enter the value to be converted on the stack in x and run the program.  The output is
given the degrees C or ohms depending on the conversion direction or supplied input.
Values given with units of ohms or degrees C will always be automatically converted.

    Example:
                     1245 THERM   --->   50_C   ( if THERM is set for  Resistance to Temperature ) 

                     50_C THERM   ---> 1245_ohms  ( regardless of how THERM is set )

Remember, values  units of will always be automatically converted the appropriate direction.
 

 >TCON allows entry and/or editing of the constants for the conversion equations  for THERM.
The constants are stored in the variable tcons.   This variable is a list containing the constants
in this order { A B C D a b c d } , refer to the references  for a description of these constants.
This program should be run after installation to create a  constants file.   While running this program,
you are prompted with two screens containing four constants each.   You must accept both screens to
store the constants.   In other words, if you cancel either of the screens the constants will not be stored.

The default values stored by >TCON are usable for many devices.  Also, the data files (cons)  supplied
may be copied into tcons to allow   THERM to conform to the device curves.   To reinitialize the equations,
in the event that an error was accepted, simply erase the tcons  file and re-run this program.

 
RTD converts between temperature and resistance for PT RTD's.  Enter the value to be converted
on the stack in x and run the program.  The output is given the degrees C or ohms depending on the
conversion direction or supplied input.   This program works the same as THERM -- if units are
supplied, the conversion is done regardless of the direction setting.
 

>RCON allows entry and/or editing of the constants for the conversion equations  for RTD.
The constants are stored in the variable rcons.  This variable is a list containing the constants
in this order { R0 a b } , refer to the reference files for a description of these constants.
This program should be run after installation to create a constants file.  The default values
stored are usable for most RTD's.

 FIT  performs a least squares curve fit on a supplied data set in order to calculate the equation constants.
This data set must be in the form of a two-column matrix.  FIT requires at least four points to curve fit the THERM
data and will calculate all eight constants.   RTD needs three or more points.  Fit will calculate a value for R0 if a value at 0 degrees
is not given.   In general, the data points should be evenly spaced and include the range to be calibrated.

To run this program, enter a data set on the stack in X and run FIT.   Next, you are prompted for the equation to fit
for either thermistor or RTD.   Finally, the respective editing program is run either >TCON or >RCON to allow access
to the constants.   Several data sets are supplied in the DATA directory for example runs. 

 
R<->T allows the default the conversion direction for THERM and RTD to be set.  The conversion
direction of each program can be toggled by pressing the appropriate key.    Setting the conversion direction allow the you to
enter and convert data quickly without specifying units.  As mentioned previously, data specified with  a unit of Ohms or Degrees C will be
converted appropriately regardless of this setting.

 TBL generates a table of values for the specified device.    TBL will prompt for the  conversion program, direction , start
value and increment.   A data table is then produced form these specifications.  
This program uses several softkeys to perform various functions they are as follows:

          Up and Down arrow menu keys increment or decrement the table by one value.

        PGup and PGdn increment or decrement 6 lines at a time.
 
        JMP allows entry of a new start value .   The current increment is used.

 INC allows entry of a new increment value.   The lowest value (top line) displayed is kept
and a new screen of values is produced using the new increment number.
When a continually smaller  increment is specified, it has the effect of "magnifying" the scale so
finer changes in the input/output relationship may be seen.

                ENTER and ON/Cancel exit the program.

Note:  TBL does not round its calculations; therefore, the display should be set for 3 to 4 digits
after the decimal place to insure proper display.

REFERENCES and BACKGROUND INFORMATION
 
        The equations used in this program were taken from the following standards:

    ASTM E 879-93  Standard Specification for Thermistor Sensors for Clinical Laboratory Temperature Measurements
    ASTM E 1137-97 Standard Specification for Industrial Platinum Resistance Thermometers.

    These standards may be obtained through  the American Society of Testing and Materials  ASTM

A very Informative group of papers regarding resistance thermometry can be found at ITS-90 PAPERS
which is part of the International Temperature Scale  website.

In addition, detailed information on thermistors and RTD's and related instrumentation can be obtained at Omega
 

Please send comments or questions to me:

Jim Purdy     jpurdy@home.com