Have use the same app and idea for heavy slurries and anything to viscous or
dirty for analog valves or where a fast adjustment was needed in any control
type scenario.
Sent from my iPhone
On Jan 31, 2016, at 23:24, Tom Vandewater <tjvandew@xxxxxxxxx> wrote:
The PTC block solution for Dirk's application had me thinking about an
application I am working on right now. There are 1st Out lights on a field
panel here and they want all of the lights to stay on and when a 1st Out
occurs they want only that light to flash on/off. This way they can tell if
any of the lights are burnt out and can also quickly locate the one that shut
them down because it will be the one flashing.
I played with the PTC block and liked what I saw until I tried to change
the frequency of the .OUTINC parameter cycle time. There is a parameter named
.REPTIM that allows you to change how often the block evaluates the error and
apply the Gain based on the PBAND setting. .REPTIM is supposedly connectable
and settable, but there is something the EDOC doesn't tell you. Changing
.REPTIM from the block detail display does not cause the PTC block to
initialize and the PTC block will store the new setting but will not apply it
until the block is initialized. Cycling the block from Auto to Manual, or
downloading a change in ICC/IACC will make it work. The PTC block WILL
accept and apply changes to all of it's other tuneable parameters such as
PBAND, MEAS, and SPT without the need to initialize the block. WTF, another
feature discovered the hard way.
If anyone is interested, here are the parameter settings you use to cause
the .OUTINC parameter of a PTC block to cycle on and off once per second when
the block is in Auto. Use all of the block default settings and just change
the following parameters as shown below:
.MEAS = 50.0
.SPT = 100.0
.PBAND = 100.0
.REPTIM = 0.0330. (Defaults to 1 minute. 0.033 minutes is 2 seconds and
.OUTINC will cycle on for 1 sec and off for 1 sec with these settings.)
If you reverse the error by flopping
.MEAS = 100.0
And
.SPT = 50.0
The PTC block will cycle .OUTDEC at the same frequency as it previously
cycled .OUTINC. With a GAIN of one, (PBAND = 100) and a 50% error between
.MEAS and .SPT the .OUTINC parameter will cycle 50% on and 50% off.
Pretty simple once you understand how it really works. Use default .5 sec
Period and don't try to set .REPTIM less than twice that time.
Cheers,
Tom VandeWater
Control Conversions, Inc.
On Jan 31, 2016, at 5:19 PM, Tom Vandewater <tjvandew@xxxxxxxxx> wrote:
I like your idea a lot Alex and it would work very elegantly too. In
Dirk's case it would require one PTC block per instance and I think he was
trying to just use one block to do all 10 but in reality 10 PTC blocks
wouldn't be much of a load on a CP270 and it would allow individual
triggering, isolation, and time tweaking of each of the 10 if needed. Tying
his continuous discrete input to the .MA of the PTC block would put the
block in AUTO when the pulse output was needed and back to Manual when not
needed. Very clever idea Alex. Maybe it just whooshed right over
everyone's head;<)
BTW, I once used a PTC block as a temperature controller for an unusual
application. As temperature increased in a still-pot it indicated the
concentration of high boilers was accumulating in the bottom. If we pumped
out the sludge/high boiling material from the pot the temperature would
quickly drop to the boiling point of the remaining material. We could've
used a continuous control valve and a PID controller except the amount of
material that needed to be removed was so small and the stream so sludgy it
constantly plugged the valve or eroded the valve seat. The eventual
solution was to open a larger ported discrete ball valve for a very short
time to drop the temperature. The PTC block was perfect for this. It
opened/closed the valve very quickly when the temperature was just a little
above setpoint and if the temperature continued to rise, would open it
proportionally longer to maintain control.
Cheers,
Tom VandeWater
Control Conversions, Inc.
On Jan 29, 2016, at 8:50 AM, "Johnson, Alex"
<alexander.johnson@xxxxxxxxxxxxxxxxxxxxxx> wrote:
No one likes the PTC block idea?
AJ
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