Analog Block Nonlinear In Programmable Out

[Harry Dellamano]

Sorry about that Harry. I thought volts/cell was nearest
the '4.699' and started from there. Ok, back to the
drawing board.

Hey Tony,
Spehro has this neat three resistor network that I SPICED at +/-1% max
error. I did a 5 resistor network before that at about the same error so I
will probably go with Sephro's.

thanks for trying
harry

 

[Harry Dellamano]

On Tue, 19 Aug 2003 16:04:23 GMT, the renowned Spehro Pefhany


Correction to the values and the error table..



T (°C) Vcell' Error (V)
-5 2.883 -0.117
0 2.802 -0.018
5 2.734 -0.006
10 2.676 0.006
15 2.628 -0.002
20 2.589 -0.001
25 2.557 0.007
30 2.531 0.001
35 2.510 0.010
40 2.493 0.013
45 2.479 0.009
50 2.468 0.018
55 2.459 0.029
60 2.451 0.041

Not so good, especially at low T, but between 0 and 55° it is
within about +/-1% of cell voltage.

Best regards,
Spehro Pefhany

http://www.speff.com

----- Original Message -----
From: "Spehro Pefhany" <[email protected]>
Newsgroups: sci.electronics.design
Sent: Tuesday, August 19, 2003 12:51 PM
Subject: Re: Analog Block Nonlinear In Programmable Out

On Tue, 19 Aug 2003 16:04:23 GMT, the renowned Spehro Pefhany


Correction to the values and the error table..



T (°C) Vcell' Error (V)
-5 2.883 -0.117
0 2.802 -0.018
5 2.734 -0.006
10 2.676 0.006
15 2.628 -0.002
20 2.589 -0.001
25 2.557 0.007
30 2.531 0.001
35 2.510 0.010
40 2.493 0.013
45 2.479 0.009
50 2.468 0.018
55 2.459 0.029
60 2.451 0.041

Not so good, especially at low T, but between 0 and 55° it is
within about +/-1% of cell voltage.

Best regards,
Spehro Pefhany
--

Spehro, you are the man, nice job. I did a five resistor network with a
little more error but yours looks like the state of the art with just three
resistors. I SPICEd it with standard 1% values and it is still close to
+/-1% max. If this is the best we can do then I will lay it on the customer.
Drinking Chimay beer right, those Trappist monks knew what they were doing
so everything looks good.

thanks S P
harry

 

[Tony Williams]

Hey Tony, Spehro has this neat three resistor network that I
SPICED at +/-1% max error. I did a 5 resistor network before that
at about the same error so I will probably go with Sephro's.

Harry, could you confirm that Vbatt table? Some of the
intervals are slightly jaggy, and that feels wrong for
an electrochemical process.

3000

-- 180 2820
-- 80 2740
-- 70 2670
-- 40 <--- ?? interval too low? 2630
-- 40 2590
-- 40 2550
-- 20 <--- ??

2530 >-- swapped?

-- 30 <--- ?? 2500
-- 20 2480
-- 10 <--- ?? interval too low? 2470
-- 20 2450
-- 20 2430
-- 20

2410

 

[Tony Williams]

This data I took was off a curve from the battery manufacture.
The data points do not form a smooth curve so there was some
measurement error. I will try to get better data but since the
data taken is not smooth this may be it.

I suspect that some of the data errors significantly affect
the 1% accuracy requirement.

Interested to see what you come up with.

It looks like the thermistor doesn't need linearising
at all.


--+--5v?
| Rt
\ +---/\/\----+
/ | |
\ +---|-\|12v |
| | | >----+--> Vout = 2.39(1 + Rt/169k)
Vref +-------|---|+/|0v
2.39V | |
\ \
/ /169k
\ \
| |
----+-------+-------0V

Vbatt Rt Vout Error
~~~~~ ~~~~~ ~~~~ ~~~~~
3000 41970 2984 - 16
2820 32430 2849 29 <-- Max +ve error.
2740 25260 2747 7
2670 19830 2670 0
2630 15670 2612 - 18
2590 12480 2566 - 24
2550 10000 2531 - 19
2530 8066 2504 - 26 <-- Max -ve error.
2500 6545 2483 - 17
2480 5343 2466 - 14
2470 4386 2452 - 18
2450 3620 2441 - 9
2430 3003 2432 2
2410 2504 2425 15

The real circuit could have a higher Vref, (and Vout
swing), with an attenuator on Vout.

 

[Tony Williams]

It looks like the thermistor doesn't need linearising
at all.

Well, the cruncher says perhaps a smidgin to get within 1%,

560 ohms added in series with Rt and the 169k changed to 174k.


--+--5v?
| 560 Rt
\ +---/\/\--/\/\--+
/ | |
\ +---|-\|12v |
| | | >--------+->
Vref +-------|---|+/|0v Vout= 2.39(1 + (Rt+560)/174k)
2.39V | |
\ \
/ /174k
\ \
| |
----+-------+-------0V

Vout mV errors.
~~~~~~~~~~~~~~~
-26, 23, 5, 0, -17, -21, -15, -22, -12, -9, -12, -3, 9, 22.
| |
-0.9% at -5C. +0.9% at 60C.