Hello,

2nd order adjustment of AD587LW#03:

since the 2nd order adjustment on AD587LW#02 took several days and T.C. runs I wanted to shorten the adjustment by simulation.

According to Lars you can use e.g. a Excel sheet to calculate. But this time I wanted to improve my LTSPICE skills.

The AD587JQ#01 reference is modeled by a temperature dependant zener (voltage source) with a output amplifier with 6K over 14K nominal.

From the T.C. measurement on 08.04.2018 I got the Zener voltage and the 3rd order LMS coefficients as:

VT=7.001525962 * (1 - (1.54472E-6*TEMP) - (1.52508E-8*TEMP*TEMP) - (8.73627E-10*TEMP*TEMP*TEMP))

Where the 7V is the raw zener voltage before amplifier and TEMP is the temperature difference to 25 deg C.

The measurement of 01.05.2018 shows that I have a convex 2nd order with 7uV height after 2:1 divider.

This corresponds to the LTSPICE simulation of about 13uV 1:1 at 10V 2nd order simulation with nominal values and 1.5Meg in series to the NTCs.

The NTCs are simulated as temperature dependant resistors with Steinhart & Hart coefficients generated by a EXCEL tool from the Vishay home page:

http://www.vishay.com/thermistors/ntc-curve-list/http://www.vishay.com/doc?29130From Lars I know that for convex 2nd order curve I have to reduce the 1.5 Meg resistor.

So I tried 680K 330K and finally 220K in the simulation.

Of course each time I have to reduce the TP2-TP1 voltage difference by the T.C. pot and adjust the output voltage to nominal 10 V.

In the diagram I have subtracted the 10V so that only the error curve is shown.

Finally I have only to read the difference TP2 - TP1 (=VTRIM) so that I know what to adjust at the reference.

A measurement on the weekend will show how near I come to the simulated "zero TC" value from the simulation.

with best regards

Andreas