tekWorx: Ask an Engineer – Differential Pressure (DP) Sensors

We at tekWorx are always willing and ready to field questions in regards to engineering, chiller plant optimization, or just about what tekWorx can do for you!

Today’s questions come from Brian…

Differential Pressure Transmitters

  1. Is it better to install the DP transmitter/sensors farthest away from the mechanical room or 2/3 away from mechanical room?
  2. Is there a recommended way/detail on how to properly install DP transmitters (or is there no way to improperly install the DP sensors)?

Thanks for the questions, Brian! Here’s some answers from one of our founders, Burt Rishel.

  1. The short answer is that the end is always better because you’re sure to satisfy every load. If you put it 2/3 of the way out, and you never have a load beyond that point that is underfed and is still satisfying the DP set-point, then you’re okay. However, if you go with 2/3, and loads beyond the sensors aren’t satisfied, you have to use trial and error to determine the set-point needed to satisfy the far load. Thankfully this isn’t a major issue unless you have a lot of diversity in that particular loop, so it comes down to the risk of an unsatisfied load and the practical installation issues.
  2. Veris PWX and PWL DP Sensors

    VERIS Industries Wet Differential Pressure Transmitters are typically recommended.

    I wish there was not a way to improperly install DP transmitters. Unfortunately, there are mistakes all the time. The most common problem is hooking up the high pressure tube to the low port on the transmitter and vice versa. The Veris model DPT we recommend eliminates this problem because the ports can be swapped on the transmitter by changing a dip switch. Otherwise, this is a relatively minor plumbing change.

    The second problem occurs when the supply and return taps are installed at different elevations. The reading will be off by the vertical difference between the taps. This is easily corrected with an offset in the program to zero out the difference. However, it’s a real problem when the control contractor is either unaware or simply does not know to take this into account.

Regards,

Burt

 

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3 Responses to tekWorx: Ask an Engineer – Differential Pressure (DP) Sensors

  1. Carol B. August 18, 2013 at 10:58

    The Veris series DPTs are nice to work with. Where I work we have standardized on the ones rated to 100 PSIG – since they are range adjustable – PWLX04S for 3 wire and PW2LX04S for 2 wire loop powered. We prefer not to use the port swap feature but it could come in handy in a pinch.

    Reply
    • Abel B Ramirez II August 18, 2013 at 15:28

      I love the Veris Wet Differential Pressure Transducers… They are built real sturdy and as you said they can be configured very easily for different scale ranges and even flip flop ports. not sure why that would be a bad thing to do the port swap since there are no external markings saying high or low, so you still have to look at where the piping is run either way.

      Reply
  2. Dan McFarland August 5, 2015 at 16:02

    “The short answer is that the end is always better because you’re sure to satisfy every load.” This is fine if the ducting doesn’t branch. Unfortunately this happens on most jobs I’ve seen so locating the sensor 2/3 down the duct is the most practical solution.

    Reply

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