Watlow EZ-Zone controllers

[Steve Bailey]

I am tasked with connecting multiple Watlow EZ-Zone PM controllers to a Watlow EZ-Zone RUI/Gateway unit. They show up to 16 controllers connected to a single gateway over an RS485 two-wire cable. I'm accustomed to putting terminating resistors at the physical ends of RS485 cables, but the Watlow manual doesn't show them on the Watlow standard bus side, only on the Modbus RTU side when you choose that option.
Does anyone have any experience with a setup like this? Can I leave the cable unterminated and reliably get the data from the controllers to the gateway?

 

[danw]

Page 6 of the gateway manual:

• A termination resistor may be required. Place a 120 Ω resistor across T+/R+ and T-/R- of last controller on network.

 

[Steve Bailey]

That note is in regard to the Modbus RTU side of the gateway when you have that option. Is it your experience that it also applies to the Watlow standard bus side?

 

[osmanmom]

http://www.watlow.com/downloads/en/manuals/EZ-RUI Rev C.pdf

page 8

 

[Steve Bailey]

I already have that manual. I know how to read it.
My question was about whether anyone has any personal experience with running the Watlow standard bus unterminated since Watlow doesn't show a terminating resistor in their manual. I found that fact to be unusual.

 

[danw]

No, no experience with this device.

But Watlow's wording suggests that Watlow has placed a terminating resistor across its terminals. I suspect that if you measure the resistance across (+) and (-) 485 terminals when the power is off, you'll find a resistance > 100 ohms.

They're probably assuming that their gateway will be at one end of the multidrop daisy chain with only the last controller needing a terminating resistor.