GHL Doser 2.1 with Director.....Doser Fried?

[Matthias Gross]

Just a few remarks:
- with a horizontal pH probe we achieved a way compacter formfactor than everyone else, just compare the dimensions of the KHD (incl. pumps) with the alternatives on the market, if the probe would be vertically the KHD incl. probe would have to be more than 20cm high, now it is 7cm high.
- this design gives you the option to either use the devices side by side or stacked, you have more flexibility
- when the nut is tightened correctly then there you will never see there a leak. I tighten it by hand (I even don't use any vaseline since I am too lazy for that) and never saw any leakage problem
- yes, the peristaltic pumps work with friction between the motor shaft and the 3 rollers, as many other vendors do, too. That's why it is not allowed to grease the pump in any way. This design is not cheap and the pumps are usually very accurate, we are talking about a repetition accuracy below 0.01ml/min (correct settings and maintenance assumed)
- I have not the slightest idea why there should have been grease in someones pump ex works. I am daily in our production and supervise what is happening there, and we never ever had any grease even near the pump head assembly, they produce tens of thousands of pump heads every year

 

[BeanAnimal]

Now, I understand that GHL wanted to house KH director in their standard "GHL box" enclosure, and that is a good thing, but does it justify a poor, potentially leaky design? I don't think so. Perhaps they could still use a shorter version of pH probe and still be able to fit in that case - I know some other manufacturers use a proprietary short probe (and that helps them charge premium for a replacement - not that I am advocate of this).

I see no problem with the horizontal design - the cord-grip style seal is proven as a bulkhead seal in countless applications and suitable here. In fact, I use the same design (larger diameter) to run the heater into the side of my sump so that the head is never submerged. You will find similar seals on NEMA rated equipment where the seal is exposed to many PSI of fluid pressure, there is no pressure to speak of in this application.

To me, the uniform modular form factor of the GHL devices is a huge selling point. The competitor and their artsy (ugly, if not obnoxious) form factor makes no sense.

As for longevity of the KH director as it relates to age or duty cycle, I can't speak to that as I have had mine for less than a year.

 

[Saith]

To me, the uniform modular form factor of the GHL devices is a huge selling point. The competitor and their artsy (ugly, if not obnoxious) form factor makes no sense.

This pretty much sums up why I went with GHL.

 

[vahegan]

Just a few remarks:
- with a horizontal pH probe we achieved a way compacter formfactor than everyone else, just compare the dimensions of the KHD (incl. pumps) with the alternatives on the market, if the probe would be vertically the KHD incl. probe would have to be more than 20cm high, now it is 7cm high.
- this design gives you the option to either use the devices side by side or stacked, you have more flexibility

True, these are great advantages, would have been unmatched, unless the danger of spilling saltwater on power lines and/or other equipment...

- when the nut is tightened correctly then there you will never see there a leak. I tighten it by hand (I even don't use any vaseline since I am too lazy for that) and never saw any leakage problem

The problem is, that the pH probe requires calibration once every few months, and this increases the chances of causing a leak, if in one of those instances the installation/tightening was not good enough.

- yes, the peristaltic pumps work with friction between the motor shaft and the 3 rollers, as many other vendors do, too. That's why it is not allowed to grease the pump in any way. This design is not cheap and the pumps are usually very accurate, we are talking about a repetition accuracy below 0.01ml/min (correct settings and maintenance assumed)

If we compare the peristaltic pumps made by one of the well-known manufacturers, Kamoer, we would see that they use the heads with friction based rotation of the rollers only in their lower end pumps. Dirt/volatile/oily substances from the air will inevitably accumulate on the rollers over time, affecting the accuracy. If you check their higher-end pumps, used for accurate dosing, designed for medical applications and/or analytical chemistry, they firmly attach to the stepper motor axis a barrel with 8 rollers. I am not even talking here about true high-end state of the art pumps, such as Wattson-Marlow, in which each roller has its own adjustable spring mechanism to control the pressure on the tube.
I also hesitate a bit about the possibility of practically achieving 0.01ml accuracy - just because the volume of a single small water drop is about 0.05ml. To be able to dose one fifth of that amount you need to use a needle, immersing the tip in water - which would then result in a diffusion leak, unless this needle is then extracted from water. What you claim is probably rather rotation angle control accuracy equivalent to 0.01ml dose.

- I have not the slightest idea why there should have been grease in someones pump ex works. I am daily in our production and supervise what is happening there, and we never ever had any grease even near the pump head assembly, they produce tens of thousands of pump heads every year

Judging by the dark color of that substance, my impression was that it has exuded from under the stepper motor shaft, perhaps during shipping, or storage. I must admit though that after I thoroughly cleaned up the rollers with acetone, I have not witnessed a similar issue in over one month of use by now. Still, I like the 8-roller Kamoer pump design much better (but they are larger than the pumps in GHL doser).

 

[Lasse]

I also hesitate a bit about the possibility of practically achieving 0.01ml accuracy - just because the volume of a single small water drop is about 0.05ml. To be able to dose one fifth of that amount you need to use a needle, immersing the tip in water - which would then result in a diffusion leak, unless this needle is then extracted from water. What you claim is probably rather rotation angle control accuracy equivalent to 0.01ml dose.

Matthias speaks about repetition accuracy below 0.01ml/min - not the accuracy in a single dose. My bold

This design is not cheap and the pumps are usually very accurate, we are talking about a repetition accuracy below 0.01ml/min (correct settings and maintenance assumed)

Sincerely Lasse

 

[BeanAnimal]

True, these are great advantages, would have been unmatched, unless the danger of spilling saltwater on power lines and/or other equipment...


The problem is, that the pH probe requires calibration once every few months, and this increases the chances of causing a leak, if in one of those instances the installation/tightening was not good enough.


If we compare the peristaltic pumps made by one of the well-known manufacturers, Kamoer, we would see that they use the heads with friction based rotation of the rollers only in their lower end pumps. Dirt/volatile/oily substances from the air will inevitably accumulate on the rollers over time, affecting the accuracy. If you check their higher-end pumps, used for accurate dosing, designed for medical applications and/or analytical chemistry, they firmly attach to the stepper motor axis a barrel with 8 rollers. I am not even talking here about true high-end state of the art pumps, such as Wattson-Marlow, in which each roller has its own adjustable spring mechanism to control the pressure on the tube.
I also hesitate a bit about the possibility of practically achieving 0.01ml accuracy - just because the volume of a single small water drop is about 0.05ml. To be able to dose one fifth of that amount you need to use a needle, immersing the tip in water - which would then result in a diffusion leak, unless this needle is then extracted from water. What you claim is probably rather rotation angle control accuracy equivalent to 0.01ml dose.


Judging by the dark color of that substance, my impression was that it has exuded from under the stepper motor shaft, perhaps during shipping, or storage. I must admit though that after I thoroughly cleaned up the rollers with acetone, I have not witnessed a similar issue in over one month of use by now. Still, I like the 8-roller Kamoer pump design much better (but they are larger than the pumps in GHL doser).

I think you are tilting at windmills regarding the horizontal pH probe. The architecture is not a problem by any reasonable measure.

Dosing pumps, I agree 100% and think the friction drive is a rather poor decision for measured dosing.

 

[BeanAnimal]

Matthias speaks about repetition accuracy below 0.01ml/min - not the accuracy in a single dose. My bold



Sincerely Lasse

I don’t agree. Yes, repeatable under ideal conditions but real world wear and dirt/contamination are a problem. Steps are steps and unless steps are missed, a direct drive (gear rationed or,1:1) is effectively a positive displacement pump. I like my dosers, but wish the heads were direct drive. I am not super pleased with the drift over time.

 

[Lasse]

we are talking about a repetition accuracy below 0.01ml/min (correct settings and maintenance assumed)

My bold

Sincerely Lasse

 

[BeanAnimal]

My bold

Sincerely Lasse

Yeah not so much that I disagree with you Lasse - I just don’t overly care for the design due to the friction variable as it relates to the diameter of the drive vs driven elements, tubIng ‘spring’ that changes with air/age and dirt/dust in the air and from particles of the rollers themselves as they wear, etc.

 

[vahegan]

I would rather boil this down that friction drive requires more frequent maintenance and/or monitoring, and hence could be less reliable compared with direct drive

 

[vahegan]

In that sense, the most reliable are these ancient Watson Marlow pumps with individual spring control for every roller.

 

[vahegan]

I don’t agree. Yes, repeatable under ideal conditions but real world wear and dirt/contamination are a problem. Steps are steps and unless steps are missed, a direct drive (gear rationed or,1:1) is effectively a positive displacement pump. I like my dosers, but wish the heads were direct drive. I am not super pleased with the drift over time.

@BeanAnimal I have tried connecting a Kamoer 24V direct drive pump to the GHL doser board, and it turns without any issues whatsoever. I checked the temperature of the driver chip onboard, and it is barely warm. So I am sure it is absolutely self to replace the pump with a suitable model from another manufacturer (I am especially willing to do this for the sample fill and titration pumps on KH Director). The only issue is that Kamoer pumps are larger in size and will have to be mounted on a panel of their own, separately. Also, they are a somewhat noisier during operation - but this is not critical.

 

[BeanAnimal]

@BeanAnimal I have tried connecting a Kamoer 24V direct drive pump to the GHL doser board, and it turns without any issues whatsoever. I checked the temperature of the driver chip onboard, and it is barely warm. So I am sure it is absolutely self to replace the pump with a suitable model from another manufacturer (I am especially willing to do this for the sample fill and titration pumps on KH Director). The only issue is that Kamoer pumps are larger in size and will have to be mounted on a panel of their own, separately. Also, they are a somewhat noisier during operation - but this is not critical.

Interesting, but in all honesty if I were going to go down that rabbit hole, I would just finish my dosing system that I designed and partially built 10+ years ago. i had the boards etched, components populated and firmware done. Just never finished the UI or assembled the dosers.

 

[vahegan]

Interesting, but in all honesty if I were going to go down that rabbit hole,I would just finish my dosing system that I designed and partially built 10+ years ago. i had the boards etched, components populated and firmware done. Just never finished the UI or assembled the dosets.

That\s it. Last mile issue. It takes a lot of effort to bring a DIY project to a complete and usable system, and the time required is never there... I am in the same boat. I had been developing my own KH meter, similar to KH director (but some principles I was planning to use were better, in my opinion), I have even started building it, but then all development stopped due to lack of time. That's why I have these pumps lying around. Then I decided that it was easier to buy GHL, as an ecosystem of its own, with all the software and hardware ready made for me and no need for tweaking (I thought). It turned out not quite so. The pumps were not as good as I expected, and of all Profilux probes, conductivity probe measures weather on the moon (they claim that's because I have not connected the controller to a grounded socket, and I think that's because they have not designed a fully isolated circuit - but this is a different story). All in all, it should take much less time to tweak an otherwise functional and complete system, rather than develop one from the scratch.

 

[BeanAnimal]

I don’t have sensor problems, but can see ground reference being an issue. A quality DC to DC converter is $10 + supporting components - a bit less in qty and in theory each input would need its own. this adds up quickly. The GHL is not cheap but the there is a reason lab grade amps/meters costs thousands and not hundreds. As much as I am not a fan of the friction drive pumps and loathe the dashboard, I think the overall offering is very solid for the price.

 

[vahegan]

A quality DC to DC converter is $10 + supporting components - a bit less in qty and in theory each input would need its own. this adds up quickly.

It's a bit offtopic in this thread, but RFM0505, isolated DC-DC by Recom, is around $1.5, and ISO1540, an I2C bus isolator from TI, is under $3 in quantities of 1000. Add to this a few SMD capacitors, all you need to complete the circuit, and you will still stay under $5 of added cost. I am sure its worth the effect, even in reduction of the number of customer tickets...

 

[Gaël]

What are you talking about?
The ProfiLux sensor inputs are correctly isolated...
Please stop making wild guesses...