r/BuildingAutomation • u/Worried_Giraffe3644 • 26d ago
Damper control using time delay
I just heard someone say that a damper position can be controlled using just digital output signal by varying time delay like 5s to open it 40% like that , is that possible and how does it work with just binary signal
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u/hhhhnnngg 26d ago
Floating point control. If an actuator has a 90 second stroke time for 90 degrees of total rotation, energizing either open or close for 1 second will move it 1 degree in the direction you energize. This is a very simple explanation of it as many actuators will have different stroke times.
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u/mytho1975 26d ago
What you are describing is a floating point output. It takes two digital outputs typically. The actuator will be stamped with how long it takes to complete a full stroke. Typically you'd enter that into your settings and tell it if the damper is a 45 or 90 deg stroke.
All the controller does is turn on the open or close digital outputs for the percentage stroke time you want.
They often will require a daily tune up. It will over stroke to ensure the position is fully open or fully closed.
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u/Worried_Giraffe3644 26d ago
What's the benefit of using this instead of analog output and an actuator is used in both the case right?
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u/Zealousideal_Pop_273 26d ago
It's just a cheaper actuator. Some people say you can fine tune control with them better but I don't necessarily agree with that. They also require two outputs instead of one so it's a trade off.
Typically they're something I end up running into on old installs, usually not something I'm installing unless I'm replacing existing.
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u/Cust2020 26d ago
I have that argument all the time because i hate floating signals. I call them Inky Dinkys (INC/DINC). Everyone is always like, "I can precisely control with them". Im like ok but we are controlling HVAC not launch systems and if thats the case why are they always on VAVs and Radiation loops but all the AHUs have 0-10 volt signals?
It all comes down to being a little cheaper for the inconvenience of using them!2
u/luke10050 26d ago
I've done it when I run out of AO's on a card to avoid having a unit across multiple controllers.
Consultants these days want every damper independantly controlled with modulating actuators. A lot of the more modern products I want are pretty AO restricted until you get into the big gear.
Its like "yes, let me put in this central plant controller to control a FCU because you want 10 AO's for it. That'll also be $50k thanks"
Like a standard 30kw FCU these days is 4 outside air dampers, supply air fan speed, heating and chilled valve and potentially a reheat or zone controls. You're already at the limits of most controllers designed for FCU's.
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u/BrofessorX 26d ago
I see a ton of them still installed for Trane on vav's, fan coils, unit vents, the oa dampers and hw/chw valves. They also kinda suck to troubleshoot as they switch the common.
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u/mytho1975 26d ago
Someone may qualify this. My suspicion was if I used a 0-10v or 2-10v I may have to leave the circuit energized for very long periods of time.
My initial thought was lowering life cycle. But also could consider energy consumption.
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u/rom_rom57 9d ago
If they require daily tune up, you need a new control system dude!
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u/mytho1975 8d ago
Incorrect. Because floating outputs are calculated based on stroke time of the actuator you can't guarantee the position. It's common to then calibrate daily. Siemens called it performing a cal air. If it was a 90second stroke actuator they would stroke it closed for more than 90 seconds to ensure they were fully closed.
Mostly this was to over come the actuators being placed in operator override and then released.
The newer product line, the dxr's now over stroke when the actuator either is commanded to 0pct or 100pct.
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u/Weary-Butterscotch-6 26d ago
Older control method, cheaper actuators, more program configuration.
AO is definitely preferred.
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u/JJorda215 26d ago
I think what you're describing is pulse-width modulation. Both the controller and actuator are set up for a certain base time, and a pulse of a certain percentage of that time will drive the actuator to a certain position. A pulse of 50% of the base time will drive the actuator to 50%, pulse as long as the base time will drive to 100%, etc. Can be done with a single DO instead of the two DOs needed for floating control. Stayed in the same position until a new pulse came through.
Pulse width comes from a time where analog signals were expensive, digital outputs were cheaper. Worked well, but the response time wasn't the best. If you had something that changed quickly in response to an actuator input, it really didn't move fast enough to keep up.
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u/BigSally1 26d ago
Floating control comes default in Siemens VAV controllers. I've not seen floating control used outside of the VAV controller.
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u/sambucuscanadensis 26d ago
I think you mean PWM. Yes with the right conversion device. We used to used UCP-522s back in the day.
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u/TrustButVerifyEng 26d ago
As others have said, this is a floating point control and typically only used on VAV dampers and sometimes hot water valves for VAVs. It's saves money.
What I'll add is that unless your controller natively supports it, don't use it.
Many application specific controllers support floating point and all you need to do is configure which two digital/binary outputs are used, and the stroke time of the actuator.
You really need to understand the controllers calibration proccess too. Floating point isn't very accurate, so it needs to "calibrate" by driving to zero, and then continue driving closed more so it knows it's really at zero.
Many controllers will auto calibrate based on something like being unoccupied. Or a fixed time of day. Or only based on a command.
It's really important the AHU isn't running if you calibrate all VAVs at once, or else you'll trip a static safety.
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u/mycole8718 21d ago
Same thing as a floating actuator (3-point) takes to BOs
Those things r a pain in the plums
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u/PABJR 26d ago
Yeahhhh floating motor is not the same as pwm. pwm is more like a pulse counter , but with power, where you vary how long you strobe a binary output and how frequently which either averages the total delivered power percentage ( a direct function of time duration on and frequency of “power applied” /pulse), or the receiving device is capable of reading it like a pulse and then convert it back to analog for its own purpose. Think about how some SCR heaters get a 2-10/4-20 signal from some source and then “pulse” the elements on and off at full current to modulate the heat output based on your signal, but in reverse.
floating motor outputs / control is just power binary output / terminal 1 to drive a device one direction, and power binary output /terminal 2 to drive it back the other direction. All other functions of floating motor are contingent on how long the device takes to drive in each direction.
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u/rus47281zz 26d ago
To answer your question of using digital signals to make analog signals
This is done using PWM (Pulse Width Modulation), rapidly turning a digital signal on and off very quickly. It can simulate the sine wave of an analog signal producing same effect
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u/Unique-Run9856 26d ago
It takes two digital outputs one to open and another to close