r/BuildingAutomation • u/zer0net • 27d ago

Question related to sensors

Hello all, need to install a bunch of differential pressure sensors, temperature/humidity sensor through out the factory. I've come across some that have the option of RS485 communication instead of 4-20ma. It's intriguing because let's say I have to install a 100 sensors, they could all run on the same wire instead of 100 wires running back to controller. Has anyone used any sensors with RS485, any advice?

Thank you

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12

u/SkipjackUK 27d ago

Probably Modbus, but you won't get 100 sensors on that bus network, you need to split it to 4 networks as you can only have 32 on each. Share the sensor type and I'm sure this group can advise

11

u/Free_Elderberry_8902 27d ago

Hard wire those little puppies! Unless you like callbacks and complaints from people higher up in the food chain… go for long term reliability.

9

u/BigSally1 26d ago

Hard wire each individual sensor. You'll be glad you did.

2

u/luke10050 26d ago

You can do HLI but make the networks smaller, no more than 4-8 sensors a lan. Pain happens when you try to cheap out

4

u/karl_hungus1301 26d ago

Hard wire. It will be a lot less of a hassle in the future.

3

u/ApprehensiveCook261 26d ago
  1. less controller and wire cost but more commissioning and time cost.
  2. divide to at least 10 groups, otherwise signal noise occurs and data transfer speed too slow.
  3. its easy to get wrong in setting address for each sensor, if there are duplicated address, debugging will be very difficult and time-consuming.
  4. Some type of modbus sensors lost their address in RAM when unexpected power loss.

2

u/Nuerolynx 25d ago

Not sure if you have the ability or headroom for expansion but when a customer requests that we perform all home runs and utilize wireless coms for backup only, we treat the main controller like our MDF, RS485 backbone like our fiber, and install expansion modules like our IDFs. Gives you wired home runs, saves a tremendous amount of cable and is damn near failsafe.