1756-DHRIO-Losing Data? Thoughts?

jasil · Jun 12, 2021

Called to a site and am neck deep currently

running, but issues.

Phase 2 completion has been running for almost 2 years no issues. Controller and comms replaced using all of the old IO because it spans many levels.

v28.11, DHRIO card, 115k, 24 remote racks.

The issue is losing INPUT data only (sporadically) for 300-400ms on multiple input cards 10-30vdc 1771-IDB.

**Voltage does not change at the input card
**Blue hose replace
*Cards replaced
*PSU replaced
*RIO adapter replaced

No node collision that the 1756 can see and all RIO adapters are always green.

Thoughts.

Ken Roach · Jun 12, 2021

OK, so your trend shows the 16-bit integer equivalent of the digital input values, correct ?

In general, if comms are lost to a 1771 I/O adapter the Input data tags remain the same; Allen-Bradley's philosophical approach to digital Inputs is always to keep the input data values at the "last state" rather than inferring comms loss by an all-zero data set, because all-zeroes is a perfectly valid state for a digital input module.

When you say "several input modules" do you mean they're all in the same physical 1771 chassis, or are they distributed throughout the system ?

Are there any other types of Input module in the affected chassis that don't appear to have all-zero inputs ?

Since you've replaced the I/O modules and the power supplies and the RIO adapters, the most likely remaining suspect is the 1771 chassis itself, or the wiring swingarms, or the DC Common connection.

jasil · Jun 12, 2021

Ken Roach said:
OK, so your trend shows the 16-bit integer equivalent of the digital input values, correct ?

In general, if comms are lost to a 1771 I/O adapter the Input data tags remain the same; Allen-Bradley's philosophical approach to digital Inputs is always to keep the input data values at the "last state" rather than inferring comms loss by an all-zero data set, because all-zeroes is a perfectly valid state for a digital input module.

When you say "several input modules" do you mean they're all in the same physical 1771 chassis, or are they distributed throughout the system ?

Are there any other types of Input module in the affected chassis that don't appear to have all-zero inputs ?

Since you've replaced the I/O modules and the power supplies and the RIO adapters, the most likely remaining suspect is the 1771 chassis itself, or the wiring swingarms, or the DC Common connection.

No, only 10-30vdc 1771-IDB's are affected.

120VAC input cards, any output cards, any analog, none of these are showing this "blip" or rapid oscillation.

Several as in 7 input cards over two 16 slot racks none of the other racks are affected.

**You bring up a very good point and you are 100% correct if I turn off the RIO adapter the IO will stay the same**

Chassis or common thanks for your input.

Ken Roach · Jun 13, 2021

Thanks for the excellent troubleshooting and details !

The fact that it's only DC input modules, and that there are no RIO protocol errors showing, argues against the I/O network. The fact that it's in two different chassis suggests its the voltage source for those sensors.

If you have put independent instruments on the DC inputs and they don't change state, that suggests to me that your independent instruments might have a connection to DC common that is closer to the power supply (or ground) than an intermittent connection in the I/O wiring.

1756-DHRIO-Losing Data? Thoughts?

jasil

Member

Ken Roach

Lifetime Supporting Member + Moderator

jasil

Member

Ken Roach

Lifetime Supporting Member + Moderator

Similar Topics