MarkMc said:
Hi Chris
I'm planning on using some small stainless steel vessels for the
'tanks' - only about 1-2 litres capacity required for each. The Will
have a metal drain, so I'll try to find a way of attaching the OSC to
this.
I was thinking about using two switches - one for manual/automatic and
another for on/off for the pump in manual mode. I assume I can just
interject these in to the collector of the relay driver transistor? I
assume switch noise isn't an issue when energising the relay?
With regards to the re-use of the pump: The brewery setup is going to
have quite a few plumbing valves, so these will be set to the required
settings before firing up the electronics. Of course, with so many
valves to worry about (see
http://tinyurl.com/bljgl), I am a bit
concerned that I'll get them wrong sometimes, so what I plan to do is
print off a couple of lookup sheets and laminate them to keep them nice
and dry, which tells me what setting each valve should be in for each
stage of my process. Brewing is a fairly timeconsuming and slow-moving
process, so it shoouldn't be difficult to make sure everything is setup
ok, especially with a checklist. It's when things start going wrong
that it gets a bit lively!
Re "in for a penny" - given no wife/family, I'd agree, but I've spent
"most of the budget" on the actual brewing equipment, so the luxury
stuff (like this control stuff), needs to be done on a budget, but hey
it's fun to do this stuff, and it's much more to talk about and show
off to your friends!
If I find I have problems with the sensors 'sensing' foam and such
like, then I'll have to re-think (the time delay will help with
spending more, I'm sure!
)
Actually, I'll be needing to update this hardware to include a heater
in one of the vessels (the underback). I was thinking I could use a
temperature controller (FE33L - Maplin, has LCD display etc - cool),
but I only want the heater to come on when the temp controller says
"too cool" (fine, theres a signal from FE33L for this @1.5v), *AND*
when the pump is on. This part I'm not 100% sure about, because the
auto/manual + on/off switching complicates things a bit.
Any suggestion on how to do this? (obviously another relay+transistor
etc) I assume some kind of AND gate with pump signal and temp ctrl?
Cheers,
Mark
Hi, Mark. Apart from just turning off the power, you can use a 3-way
SPDT switch (ON-OFF-ON) to give you both the pump OFF and pump OVERRIDE
functions like this:
`
` VCCVCC
` + +
` | |
` - C|
` ^ C|
` | C|
` | |
` '--o
` |
` Logic | Override
` o | o
` | |
` ___ |/ Pump |
` -|___|-o-| Off ===
` | |> GND
` .-. |
` | | |
` | | ===
` '-' GND
` |
` |
` ===
` GND
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta
www.tech-chat.de
The switch actually has three positions -- up, middle, and down. In
the middle position the switch pole isn't connected to either throw.
That makes it an ideal, relatively easy hardware solution.
When you have any kind of low voltage high input impedance sequential
logic, static from machine operators and moving parts and electrical
noise can be a PITA, changing logic states and damaging ICs. Actually,
as the prices of PLCs (Programmable Logic Controllers) came down to
reality in the early 1990s, I basically stopped doing any factory
industrial control circuits with 4000-series CMOS just for that reason.
PLCs generally have optoisolated inputs and RC filters on the inputs
to reduce the chance of electrical noise or ESD getting through. And
again, this is another good reason for using a float. It's not
affected by any of this stuff. But there are ways to deal with EMI/RFI
in CMOS circuits...
First, you obviously wouldn't have any chance at all if the FF inputs
were just hanging out in the breeze. But the caps and the schmitt
trigger inputs condition the "real world" inputs and will effectively
prevent electrical noise from affecting them (assuming you're using
good caps and your circuit layout has a good low impedance ground
path). Noise might affect the FF itself, though.
In order to minimize the risk of that occurring, you can do several
things. The first and most important thing is to try to prevent the
inductive kick of the pump switching off from creating a big spark that
will cause EMI. To do that, you should place a snubber across the
load. For AC loads (you are using an AC pump, right?), you should use
an R-C snubber across the load.
`
` ||
` .-------||----o------o------.
` | || | | |
` | RY | | .-. |
` | .-./ R| | |Pump
`240VAC _ | / | | C|
` / \ MOV |/| '-' C|
` ( ~ ) / | | C|
` \_/ /'-' C | |
` | | | --- |
` | | --- |
` | | | |
` '-------------o------o------'
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta
www.tech-chat.de
You want to choose an R based on the maximum switching current of your
relay. Let's say you've got 240VAC, a 5 amp relay contact, and a 1/2
amp pump. You then want a value for R which will bring the current
fairly close to the rated current. If you use 100 ohms, that will get
you to about 3 A switching current. You can then choose a value for C
(line-rated cap, of course) which will just keep the relay contacts
from arcing. For relays with clear cases, you can actually watch the
arc disappear as you increase the value of C. For enclosed relays, you
should remove the cover to check. You didn't mention pump current, but
I'll guess it's rated for less than half an amp. For that sized pump,
I would start with 0.1uF and see what happens. Among my trove of
delightful stuff I've got a small box of different sized Quencharcs to
just plug in and see what works. But it seems ITW/Paktron is having
difficulty with getting distributors for their product these days, so
you'll have to use discrete parts. Try the Cornell-Dubilier MMP6P1K
(0.1uF, 600V, self-healing polyester film, you can get this from
Farnell if you reference Newark P/N 95F7892) and a 100 ohm 1 watt or
greater resistor.
Unless you've got a particularly large pump, this should do the job.
To make it just about the perfect snubber, put a 280VAC rated MOV
across the R-C snubber (the bigger the better - physical size on MOVs
is proportional to joule rating). That will prevent the voltage across
the cap from exceeding the rated voltage on the inductive kick, which
will basically mean the snubber will last forever. It's preferrable to
put the snubber/MOV across the load, but if that's not practical, you
can put it across the relay contacts.
Having reduced or eliminated the relay spark, it's still better to put
the relay physically as far away from the logic circuit as practical.
The worst thing you can do is use a PC mount relay, and put the relay
right next to the FF IC (don't laugh -- I did it once long ago). To
quote from the wisdom of '70s vintage Sesame Street, "The Solution...
To Pollution... Is Dilution". If you've got a source of EMI/RFI
pollution, the farther away it is, the lesser effect, the better. It
might even help to mount the relays for the control logic in another
enclosure next to the pump, and have low voltage control lines going
from the controller box to the relay box.
On the IC side, there's a few things you can do. Bypass the Vcc pin of
each IC with an 0.1uF ceramic cap to GND. Keep the wires of the FF as
short as possible, by using two NORs on one side of the IC and using
direct wiring there.
Between working on the relay (EMI source) and the IC (EMI target), you
should be in pretty good shape. Experiment around a little here once
you've constructed this. Try switching two pumps if you have them, and
see if this affects things. If you don't have two pumps, try putting a
greater load on the pump (momentarily lock the rotor or put a friction
load on) and see if the increased noise causes the logic circuit to
upset. This isn't a proof that your solution works, but it helps to
give confidence in the work you've done. The fact is, a hobbyist
doesn't have the tools to really solve this kind of problem, so the
best you can do is build up a lot of protection, test it as best you
can under real world conditions, and then hope for the best. But with
only one FF on one IC with no inputs extending from the immediate area,
you shouldn't have much to worry about after you do the above stuff.
Your little controller board (amazingly, only 10 pounds!) seems to have
a logic level output for heating. Again, you can use relay logic to
make sure the heater is on only when the pump is on like this:
`
` || ||
` .-------||----o------o------o------||------.
` | || | | | || |
` | CRY1 | | .-. | CRY2 |
` | .-./ R| | |Pump |
`240VAC _ | / | | C| .-.
` / \ MOV |/| '-' C| Heater| |
` ( ~ ) / | | C| | |
` \_/ /'-' C | | '-'
` | | | --- | |
` | | --- | |
` | | | | |
` '-------------o------o------o--------------'
`
`
` VCC VCC
` + +
` | |
` - C|
` ^ C| RY2
` | C|
` | |
` '---o
` |
` LO from ___ |/
` FE33L >-|___|-o-|
` | |>
` .-. |
` | | |
` | | ===
` '-' GND
` |
` ===
` GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta
www.tech-chat.de
The .pdf file referenced on the Maplin page doesn't say much about the
sensor itself. You have to be careful about installing it in a food
service environment, though. This requires some looking into. Another
issue might be that the module will have a "bang-bang" output, which
means that it turns on the heater when the temp is too high, and turns
off when it's too low. There's no proportioning of the output, which
might cause pretty major oscillation in liquid temperature -- in fact,
it might make it worse than not having any controller at all. If you
adjust so the water starts at a certain initial temperature, it may be
better to control the temperature of the liquid by just using a lamp
dimmer in series with the heater, replacing CRY2 directly in the
circuit above, and keeping it at a setting that will keep the
temperature fairly stable. You can then use the FE33L as a temp
display only. Don't know. Could use some more information here. Or
even better, one or two good experiments with tap water before you brew
anything.
Hmmn. Home brewry vs. wife -- a difficult choice. I'd have to think
'er over a while. ;-)
Cheers!
Chris
