fan operation without EFA Planewave CDK14 · Yuxuan · ... · 221 · 4141 · 24

Yuxuan:

Ruediger:

Yuxuan:
From anecdotal evidence I heard from a 12.5" CDK user in Louisiana (with high humidity), Pegasus UPB worked well for him in controlling dew while the native Delta T failed.

Easy to explain: UPB works with dew point, whereas the Delta-T either overheats or kicks in far too late. Any solution (or work around) using a humidity sensor is superior to the native solution.

PWI3 lets DeltaT heat the primary backplate to a certain temperature above ambient, but it's not the backplate that dews... (insert facepalm emoji here)

On the AGO iDK, the control logic is to heat the (edge of the) primary mirror to a certain temperature above ambient. Even without measuring humidity the heater works well for me in humid Florida.

But the primary mirror temperature isn't known by DHM. So how is it keeping the primary mirror temperature to a certain amount above ambient? All DHM knows is ambient, humidity, and secondary mirror temp.

Ruediger:

Ruediger:

Yuxuan:
About the series-5 controller, currently it only works with series-5 focuser/rotator on the Delta Rho, but PW has hinted to me that it may be adapted for CDK14 and up with Hedrick focusers. I think in order for them to come to their senses customer demand is key.

Right now they insist that the current EFA+DT combo works well for many of their scopes up to 1m ones deployed around the world. I doubt it in very humid climates, but I tend to agree with them for a setup in, for example, New Mexico.

That’s what they had told me too - until I have proven by evidence that it cannot work under some conditions. After that they admitted they never tested it under less optimal conditions.

I gave up on that point. DHM works for me now, but the basic concept fails by design. 

CS
Rüdiger

What is DHM? I saw this mentioned before, is this a new software solution that helps make Delta-T more useful?

After more than a year back and forth, PWI accepted that it does not work in my climate conditions and a lake of water in the tube. They have provided (as work around) an additional piece of software which can evaluate an ASCOM humidities sensor and controls fans and heaters based on the dew point instead of temperature only. This was never officially published, since „everything works so great“ 🤪

Only with DHM (Dew Heater Manager) I can run the CDK in my climate conditions, which is actually quite average.

The link Rouz provided earlier has a download for Dew Heater Manager 1.0.0 and 1.0.1. I have downloaded them both.

Link: Index of /files/tools (planewave.com)

So, if I understand you correctly, this can use any ASCOM Observing Conditions driver to evaluate humidity data to make decisions about operating the heaters and fans? If so, how does it then tell the fans to run? I thought the EFA was needed to interface with the fans? 

Does this run on its own or do you run with the other PWI3/4 software?

Rouz Astro:
I spoke to PW and asked if they could change the software to use the backplate temp., they were not to happy that we are using his software as it wasn't meant to be public and more of Beta.

Yuxuan:

Willem Jan Drijfhout:
I believe the Delta T can use 'backplate' temperature for that, a kind of proxy for ambient. Based on graphs that Ruediger published earlier, secondary seems highly variable, so not a good choice. Whichever temperature used (even with primary mirror measurements using EFA), none is ideal, as it does not take into account humidity and therefore dew point. That is where John Hayes's electronics comes into play to solve. 
Otherwise (and that is how I plan to use it for now) it is a matter of turning on at a fixed %, and experiment with what setting works generally well under you local conditions. 
It would be interesting to hear Rouz's latest experiences. I believe he even ran it (for a short while?) without a Delta-T at all, and just used UPB to control power to the heaters.

Yeah if I've learned anything here the solution @John Hayes designed is the best way to approach and solve this significant design flaw. I would be happy to pay for one, or build one from a set of instructions. 🙏

In lieu of that, I guess people without the EFA and only Delta T are using the backplate temp to trigger heating the primary for some random amount of time?

I just realized that I don't fully understand @John Hayes 's approach. Is the control logic the following?

if TDPS<6C then 

     PassThrough (DeltaT)

else HeaterOff

If so, what is the ambient-secondary and ambient-backplate temperature difference set in the Delta T?

Rouz Astro:

Ruediger:

Ruediger:

Yuxuan:
About the series-5 controller, currently it only works with series-5 focuser/rotator on the Delta Rho, but PW has hinted to me that it may be adapted for CDK14 and up with Hedrick focusers. I think in order for them to come to their senses customer demand is key.

Right now they insist that the current EFA+DT combo works well for many of their scopes up to 1m ones deployed around the world. I doubt it in very humid climates, but I tend to agree with them for a setup in, for example, New Mexico.

That’s what they had told me too - until I have proven by evidence that it cannot work under some conditions. After that they admitted they never tested it under less optimal conditions.

I gave up on that point. DHM works for me now, but the basic concept fails by design. 

CS
Rüdiger

What is DHM? I saw this mentioned before, is this a new software solution that helps make Delta-T more useful?

After more than a year back and forth, PWI accepted that it does not work in my climate conditions and a lake of water in the tube. They have provided (as work around) an additional piece of software which can evaluate an ASCOM humidities sensor and controls fans and heaters based on the dew point instead of temperature only. This was never officially published, since „everything works so great“ 🤪

Only with DHM (Dew Heater Manager) I can run the CDK in my climate conditions, which is actually quite average.

The link Rouz provided earlier has a download for Dew Heater Manager 1.0.0 and 1.0.1. I have downloaded them both.

Link: Index of /files/tools (planewave.com)

So, if I understand you correctly, this can use any ASCOM Observing Conditions driver to evaluate humidity data to make decisions about operating the heaters and fans? If so, how does it then tell the fans to run? I thought the EFA was needed to interface with the fans? 

Does this run on its own or do you run with the other PWI3/4 software?

*It needs an ASCOM RH sensor and reading but the main issue is that it needs the primary temp provided by the EFA.
With the Delta T you only get the backplate temp and the software didn't work for me.

I spoke to PW and asked if they could change the software to use the backplate temp.,  they were not to happy that we are using his software as it wasn't meant to be public and more of Beta.

So how have you been heating the primary mirror?

John Hayes:

Yuxuan:

Willem Jan Drijfhout:
I believe the Delta T can use 'backplate' temperature for that, a kind of proxy for ambient. Based on graphs that Ruediger published earlier, secondary seems highly variable, so not a good choice. Whichever temperature used (even with primary mirror measurements using EFA), none is ideal, as it does not take into account humidity and therefore dew point. That is where John Hayes's electronics comes into play to solve. 
Otherwise (and that is how I plan to use it for now) it is a matter of turning on at a fixed %, and experiment with what setting works generally well under you local conditions. 
It would be interesting to hear Rouz's latest experiences. I believe he even ran it (for a short while?) without a Delta-T at all, and just used UPB to control power to the heaters.

Yeah if I've learned anything here the solution @John Hayes designed is the best way to approach and solve this significant design flaw. I would be happy to pay for one, or build one from a set of instructions. 🙏

In lieu of that, I guess people without the EFA and only Delta T are using the backplate temp to trigger heating the primary for some random amount of time?

I just realized that I don't fully understand @John Hayes 's approach. Is the control logic the following?

if TDPS<6C then 

     PassThrough (DeltaT)

else HeaterOff

If so, what is the ambient-secondary and ambient-backplate temperature difference set in the Delta T?

Bill,
That's the basic idea but it's implemented in a slightly more sophisticated way.  If you were to simply implement the simple on/off logic that you listed, the controller could oscillate when the measured DeltaT is near 6C.  Instead, my controller implements a "latched" switch.  The heater is set to ON when DeltaT falls below the specified threshold (in this case 6C) and that event resets the value needed to turn the heater OFF.  My latch value is 1C, which means that DeltaT has to go above 7C for the heater to turn off.  My controller also includes a status monitor and command processor so that it's easy to manual control things if necessary.  It checks for measurement mismatch between the two sensor to detect errors and the sensors are connectorized to make them easy to change in the field.  At the moment, one of the sensors on my  20" controller has gone bad so I'm taking a bag full of them to store at the site to make replacement easy.

I typically set the ambient-backplane temp difference in the DeltaT to 3C and that seems to work well.  When I look at the data in the morning and see that the primary and secondary temps are a constant 3C above ambient, I know that the heaters were turned on.  This worked well for a few month before I visited the observatory last February.  There were water drop trails through the dust on the sides of the scope but the mirrors were perfectly clear.  I'm heading out there again in another month so we see how it looks after more than a year.

I'll send you an email about what I can do to help you out with your new scope.

John

Ruediger:
But then I wonder, why they put DHM on there file share for public access. That does not match.

Yuxuan:
I highly encourage every user who's not satisfied with the current solution write to PW and ask for an update. At some point I was told in principle series 5 control box can be adapted for CDKs including the CDK12.5, but the CDK12.5 adaptation is not currently under consideration because of lack of customer demand.

PW's customer service has been very responsive and helpful. But in my communication with them on this matter, I feel that their lack of motivation comes from a false sense that their current solution works extremely well and no competitor is even close.

While I do not dispute that, here is what their website says:



The content in the "Description" section is completely wrong, misleading, and would lead one to reasonably believe that the Delta T does stuff it does not do without the purchase of a second product the consumer would not otherwise purchase. You cannot monitor the current temperature of the primary mirror and surrounding ambient temperature with the purchase of the Delta T product alone. You must buy the EFA product, which costs MORE than the Delta T product does.

This is bad business practice and is an anti-trust violation, read more here:

Tying the Sale of Two Products | Federal Trade Commission (ftc.gov)

It is not reasonable for a consumer to purchase an optional controller box for an optional focuser to get their optional Delta T unit to work as advertised here. No one should support what they are doing or make any excuses for them. They really, really need to fix this problem and provide impacted customers with a path to the results they promised the Delta T product would deliver on its own, which they have clearly called out here in this example.