Control of heater circuit part2

[John Fields]

On Sat, 17 Apr 2004 11:00:36 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

John Fields wrote:

Schematic on alt.binaries.schematics.electronic.


I am not sure this works as intended- as the exterior temperature falls,
U4B output falls too- gained up by the "slope setting"- and this lowers
the setpoint threshold on U5B IN(+) causing the boiler to cut out at a
lower rather than higher temperature.

---
You're right, thanks.

Looks like U4B needs to be an inverting differential amp with a fixed
offset and gain variable with the slope control. Should be done some
time today...

--
John Fields

 

[John Fields]

On Sat, 17 Apr 2004 08:29:22 -0500, John Fields
<jfields@austininstruments.com> wrote:

Looks like U4B needs to be an inverting differential amp with a fixed
offset and gain variable with the slope control. Should be done some
time today...

---
Done and posted to abse.

--
John Fields

 

[Fred Bloggs]

John Fields wrote:

On Sat, 17 Apr 2004 08:29:22 -0500, John Fields
jfields@austininstruments.com> wrote:



Looks like U4B needs to be an inverting differential amp with a fixed
offset and gain variable with the slope control. Should be done some
time today...


---
Done and posted to abse.

Yep- that works now- except that pot labeled Boiler Setpoint 20-80 is
now a slope adjust too- and not needed. He only needs the slope adjust
pot- the 20oC is implicit:
Please view in a fixed-width font such as Courier.



i
n |
t |
e | \
r | \ oC interior above 20
i | \ Gain= --------------------
o | \ oC exterior below 20
r | \
| | \
| | \
s | +---\ 2
e | Gain \ \ /
t | \ 1 3
p | \ /\
o | \ ( )
i | \ --
n | \ Gain Pot Dial
t | \
| \
+-----------------+--
(0,20) exterior temp (20.20)

 

[John Fields]

On Sun, 18 Apr 2004 12:03:59 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

John Fields wrote:
On Sat, 17 Apr 2004 08:29:22 -0500, John Fields
jfields@austininstruments.com> wrote:



Looks like U4B needs to be an inverting differential amp with a fixed
offset and gain variable with the slope control. Should be done some
time today...


---
Done and posted to abse.


Yep- that works now- except that pot labeled Boiler Setpoint 20-80 is
now a slope adjust too- and not needed.

---
Not really a slope adjust as much as a setpoint control, but since
it's the outside temp which is supposed to be controlling the boiler
temp in conjunction with the slope control, you're right. It has no
business being there. I'll post the final(???-) schematic to abse in
a few minutes.

--
John Fields

 

[John Fields]

On Sat, 17 Apr 2004 13:26:54 +0100, Tony Williams
<tonyw@ledelec.demon.co.uk> wrote:

In article <s5e180lq0k0jlgjcu1i8iia7hv0aalo4n1@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:

80 +---+---+---+---+---+---o
| | | | | | |
70 +---+---+---+---+---o---+
| | | | | | |
60 +---+---+---+---o---+---+
| | | | | | |
BOILER TEMP, °C 50 +---+---+---o---+---+---+
| | | | | | |
40 +-------o---+---+---+---+
| | | | | | |
30 +---o---+---+---+---+---+
| | | | | | |
20 o---+---+---+---+---+---+
20 13 7 0 -7 -13 -20
APPROXIMATE OUTSIDE TEMP, °C

Isn't that graph a straightfoward boiler setpoint offset?

T_boiler = 50 - 1.5*T_outside.

---
As long as the slope is understood to be dy = 1.5*|dx|, I guess so...

--
John Fields