Hello again,
Ok i understand now what you want to know. The short answer is 'yes', but there are ways around this, and one of them is to make R30 equal to 100k, leave the other ones alone except change the second stage gain to 2.1 and that's about it except for the error calculation which you'd like to know.
In the following R29a is the resistance of the upper portion of the pot and R29b is the resistance of the lower portion of the pot. We can then just set R29b and calculate R29a from:
R29a=R29-R29b
To start, first we set Vin=0 and adjust R29 to provide 0.2 volts output. This leads to a value of R29b:
Code:
R29b=(sqrt((3600*G^2*R31^2+((4-120*G)*R29+(4-120*G)*R28)*R31+(4*R29+4*R28)*R30+R29^2+2*R28*R29+R28^2)*R32^2+(((4-120*G)*R29+(4-120*G)*R28)*R31^2+((8*R29+8*R28)*R30+2*R29^2+4*R28*R29+2*R28^2)*R31)*R32+((4*R29+4*R28)*R30+R29^2+2*R28*R29+R28^2)*R31^2)-60*G*R31*R32+R29*R32+R28*R32+R29*R31+R28*R31)/(2*(R32+R31))
With the values i suggested, this leads to a value of R29b of 1688.9475 Ohms.
Now to see the output error, we can calculate the output with Vin=0 and with Vin=1 and we get:
Vin=0, Vout=0.200
Vin=1, Vout=10.206596
The equation that includes the two pot values is:
Code:
Vout=G*((R29b*Vref*R31+Vin*A*R28*R30+R29b*Vin*A*R30+R29a*Vin*A*R30+R29b*Vin*A*R28+R29a*R29b*Vin*A)*R32)/(R28*R31*R32+R29b*R31*R32+R29a*R31*R32+R28*R30*R32+R29b*R30*R32+R29a*R30*R32+R29b*R28*R32+R29a*R29b*R32+R28*R30*R31+R29b*R30*R31+R29a*R30*R31+R29b*R28*R31+R29a*R29b*R31)
Now you see the error is about 0.007 volts at full scale which is a tiny percentage of full scale, and about 3 percent of the offset.
If this isnt good enough, then we could do a simultaneous solution of both the correct pot setting and R31, and doing so we'd come out with roughly the same value for the pot setting and the value of R31 would change by about +20 ohms (roughly), and that represents 0.2 percent (two tenths of one percent, not 20 percent) so now we are down below the tolerance of the resistors.
But if you wanted to adjust that resistor too you could do that too. To accomplish this you would adjust R29 and then R31 and then R29 and then R31 again. But since the percentage is so small i dont think it would pay to bother. It's up to you though.
Does this make sense now? I think i addressed your second question a bit better this time, but no problem if you have more questions. I could also do a more exact analysis tomorrow sometime for the error and resistance percentage change required.