Re: [foxboro] My RTDs don't go below zero

Here is a reply from the Foxboro knowledge database.............1991 vintage
...... use SCI=43

DESCRIPTION OF DIFFICULTY: RTD INPUT. 
100w PLATINUM RTDs .00385 ALPHA USING SCI=42 THE AIN BLOCK GOES BAD I/O
BELOW 0 DEGREES C. .
 IF SCI=43 TEMPERATURES BELOW 0 DEGREES C CAN BE MEASURED WITHOUT ANY
PROBLEM. ** NOTE FROM TAC TO ENGINEERING: PREVIOUS RESPONSE TO DUPLICATE OF
THIS ISSUE (CAR 0522) WAS: "NOT A PROBLEM; SCI=42; IS A DIN STANDARD WHICH
ONLY GOES TO AS LOW AS 0 DEGREES C. USE SCI=43 TO GO UPTO -200 DEGREES C" 
IN THE I/A CP ALL THEMOCOUPLE (20-28) AND RTD (40-44) SCIX ARE DERIVED
EXCLUSIVELY FROM THE NBS (NATIONAL BUREAU OF STANDARDS) EQUATIONS AS
DESCRIBED IN NBS NOMOGRAPH .SCIX-42 IS 'OLD' DIN43760-1968 WHOSE EQUATION
WAS NEVER OK'd FOR USE BELOW 0 DEGREES C. SCIX-43 IS THE 'NEW' DIN43769-1980
(IEC) WITH EQUATIONS DEFINED OVER THE -200 TO 850 DEGREE C RANGE. DIN, BS,
ANSI-ASTM, AND JAPAN ARE ACCEPTING THESE VALUES AS THEIRS ALSO. AS FOR TI
5-26a, THE VALUES BELOW 0 DEGREES C WERE SIMPLY CREATED BY FOXBORO. FOXBORO
ANTICIPATED THAT THE 'OLD' DIN WOULD BE ACCEPTED BY NBS FOR USE IN THE
CRYOGENIC RANGE SO THEY SIMPLY COMPUTED THE 'OLD' DIN EQUATION DOWN TO -200
DEGREES C FOR TI 5-26a. 


>  -----Original Message-----
> From:         foxboro-bounce@xxxxxxxxxxxxx   On Behalf Of "ZIEGLER, JOHN
> E" <JEZIEGLER@xxxxxxxxxxxxx>
> Sent: Tuesday, February 25, 2003 10:05 AM
> To:   Foxboro Mailing List (E-mail)
> Subject:      [foxboro] My RTDs don't go below zero
> 
> 
> We have found that our RTDs don't read below zero.  Is there some I/A or =
> instrument related issue that can explain this?
> 
> Our RTDs are directly wired to an FBM03.  The AIN block has an SCI of =
> 42.  It has a scale configured to show -10 deg C to 150 deg C.  We are =
> using 6.1.1 software.
> 
> When the measured temperature is below 0 deg C, the block shows I/O bad.
> 
> Thank you for your help.
> 
> Jack Ziegler
> Sunoco Chemicals
> Frankford Phenol Plant
> Margaret & Bermuda Sts
> Philadelphia, PA 19137
> 215-537-2455
> JEZiegler@xxxxxxxxxxxxx=20
> 
> 
> 
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