Reply to Thread

great info. here

Originally Posted by whec720

Learning a lot from this thread. I'm by no means a controls guy, but have looked up why floating point is claimed to be superior at less wear than that of an analog actuator. I'll let you guys debate the facts and will just shut up and read. Great posts, BTW.

In the case of the common Belimo actuators, I believe the mechanical parts are essentially the same between the analog and floating point actuators. What is different is simply the built in electronics of the device. I could be wrong. I've never asked Belimo. But I have disassembled a few non-working actuators out of curiosity and the mechanical parts looked identical to me.

I'm personally unconvinced that there is any significant difference in wear over time between the two, based upon any difference in design.

However ...

I have on a number of occassions seen situations where an analog Belimo actuator was doing some excessive hunting (minor, continual movements) as a result transient, induced voltage fluctuations on the signal wire. Exact source of the induced fluctuations, I most often did not determine. <Shrug> No time to fool with it and investigate.

When such a situation was found, I'd usually ensure that ....

1. Common on the actuator 24 VAC power supply and common for the signal source ... were in fact common to each other.

2. Check for differences in ground potential between equipment at which the actuator was mounted and where the controller was mounted. ie At one job site controller was mounted (and grounded) inside building envelop inside a storeroom and Belimo was attached to a rooftop unit. Actuator was "wandering". I ran a wire from controller enclosure up to roof and attached it to RTU metal. Checked with voltmeter, from ground of controller to ground of RTU and found a varying voltage differential. Only a few volts, but it was there. Bonded my temp wire to frame of RTU and to same ground controller used. Problem went away.

3. Occasionally have found small, nuisance induced voltage on signal wire (yes, it was shielded and shield drain wire connected to common at controller) which was corrected by simply readjusting minimum output voltage of controller analog-out signal from 2.0 VDC down to 1.8 VDC (for example). How and why small fluctuations were occurring despite a constant commanded voltage output ... who knows? I don't. Doesn't happen often but I've seen it, time to time. Usually haven't the time to investigate in detail.

I've noted that floating point actuators, by the nature of how they work, don't have this problem. Rock steady, transients don't effect them.

But as noted, either analog or floating point motors CAN BE severely affected and excess wear occurs if the control loop allows too frequent position readjustment (hunting). I always purposely design in a slow response in the control loop and a healthy deadband. After all, does it really matter, in the case of dampers and valves, in average comfort HVAC applications, if one sets up a control loop that allows a half degree, or even a full degree, of temperature swing off setpoint before a valve or damper moves? The fact that you CAN control to much tighter tolerances ... does NOT mean it's a good idea. Or even worthwhile. Is the increased wear and tear worth the results? Not often.

Just my opinion, worth no more than that.

...........I OFFICIALLY PROCLAIM ALL YUS.....NERDS!

A 4-page thread on FP?!!!!

bUT i LOv IT.....

meter use

I have two d.m.m.'s on my truck, a Fluke 179 & a Fluke 16.
The Fluke # 16 has a feature that they call lo-z or something like that. If you connect to a triac with the meter in ohms range it'll auto-switch to this lo-z mode and dampen the "ghost voltage" to a reading of zero, if the triac is closed (on) then the reading will show the voltage like a normal meter would. My 179 was expensive (for me) but I grab the less expensive 16 ($120.00) 90% of the time. I used to use the relay test until I discovered this feature on my meter.

I've never tried it, but couldn't you use a clamp-on ammeter on each of the actuators "open" and "close" wires to see which has the greatest amperage?
Then compare it to the common wire amperage for reference.
jogas

Interesting Thread

Learning a lot from this thread. I'm by no means a controls guy, but have looked up why floating point is claimed to be superior at less wear than that of an analog actuator. I'll let you guys debate the facts and will just shut up and read. Great posts, BTW.

This system and method receives input command signals from an actuator controller, and effectively integrates these signals until the controller has requested a large enough movement of the actuator that the actuator can actually effectuate. At this point, the system and method drive the actuator to the commanded position. As a result, excessive mechanical wear in the actuator caused by small command signal perturbations and dither is reduced or eliminated.

Intgeresting Thread

Double post. My apologies.

>constantly reposition a vav damper to maintain the airflow setpoint, it means the rest of your system is not setup properly.

Ditto, you have other issues to look at. Also moving an electronic actuator in this manor will reduce its life regardless of the type.

And the word from Mr. Belimo on the life expectancy of the different types…

“No difference.

We test all the actuators the same. The new generation non-spring actuators, i.e., LMBs, are all tested for 100,000 full open-closed cycles and 1,000,000 partial cycles.

I don’t see any noticeable difference between the -3 and –SR.”

That’s lines up with what I have seen over the years. Properly applied and installed they will most likely outlast the controls driving them.

I agree, if you have to constantly reposition a vav damper to maintain the airflow setpoint, it means the rest of your system is not setup properly.

Personally, I like analog better than floating for many reasons, however as most people, I use floating vav actuators for many other reasons...

Why is a floating point going to last any longer than an analog actuator? A 0-10v is going to compare the input to its current position. If they differ it moves, otherwise the motor is at a stop. I guess the position pot could wear out. I’ll ping our rep for the MTBF between these, you sparked my interest to see if this theory holds water.

More accurate, only if your controller can track the time accurately enough and pulse its outputs for < 1/3 second when needed. Belimo’s analog versions have 256 steps over the stroke they can land on. That’s .37deg increments you could modulate to if necessary. Trying to move it in smaller increments I would think backlash in the gear train is going to throw off the position. This would make trying to position it that accurately useless.

I would be interested in hearing a story how moving a VAV damper by <0.4&#37; of the total stroke solved a comfort issue. Grossly oversized equipment?? Not trying to be arrogant, just realistic.

BTW I based my math on the LR24-3 that sparked this thread. 95deg stroke in 95 seconds.

Floating actuators aren't just cheaper as a reason to use them on large quantity applications like VAV, they are better than modulating for VAV. The life is much longer and the floating is more accurate with small repositions.

Cool.........thanks

An important step that hasn't been mentioned is how to test the triac with a meter in the absence of a relay or the time to wire one in.

Triacs will leak, sometimes almost as much voltage as it would take to energize a coil on a relay but just enough to not. You need to measure the voltage at the triac, in this example 24.7v. Then measure the power source for the board powering the triac, lets say a transformer. We will fcall that the reference voltage. If the transformer is putting out 28.1v then the relay should not energize until the triacs output voltage is equal to the reference voltage.

As far as testing the actuator at the actuator, a lot of times we would ire 24v to the common and we would switch the ground of each output, open and close. Measure common of the actuator to earth ground (the can) and if it is good then jumper that common 24v to the open and it should stroke open, repeat for close.

Hope it helps.

Originally Posted by rolo

happy to help you

How did you help? I believe all the credit for help goes to the people that actually read the thread and posted responses pertaining to the thread.

It is nice to see that you didnt call something junk or recommend Robertshaw for a change.

happy to help you

You have snatched the pebble from the hand!

Very good grasshopper.

Glad you found your problem!

In case anyone was curious....... when looking at the program with "Anywhere" it showed one valve with a stroke time of 30sec.......... should have been 110 or 120, when changed it operated good. Thanks for the help all.

Many that I have seen (where I know the software) tend to drive the output closed for twice the specified drive time when the unit moves out of occupancy.
There was also a manual stroke routine to achieve the same effect. It really ought to be automated so that it can be periodically nudged, in my opinion.

Wow floating point is about beat to death! This should become a sticky.

>When it calibrates ... does it indeed sense the resistance when it runs into a mechanical stop, or does it simply run it in one direction long enough that it knows it should be at full stroke?

Varies manufacture to manufacture. One thing is sure, they don't measure resistance or anything that fancy. Typically they will overdrive the actuator by more than enough to be sure it’s all the way. ie if its a 90sec actuator it may be driven for 120 to sync it.

Another method is to just keep pulsing the output when the controller thinks the actuator is 100% or 0%.

Some controllers will take a feedback from the actuator, pot or contacts. Haven’t seen this method much lately.

Floating point is meant to be cheap, nothing more. 2-10v or 0-10v actuators cost more, and when you need 100+ for VAVs etc it adds up quick.

>most people do have an extra 24vAC relay banging around somewhere, so its a quick and easy tester. I can hear people laughing at me now... O'well

Ditto, I like the RIB relays as emergency backups. Dual voltage 24/110 coils with indicator light make them especially useful.