Rosemount 848L Logic Transmitter performance

[richard john]

Dear readers,
The Rosemount 848L Logic Transmitter has particular importance in a design proposal for an electrical SCADA system. Majority of signals will be discrete inputs.
Can users with similar applications share their experiences i.e. monitoring of MCC and switch gear status on the Delta V system?
e.g. susceptibility of EMI on the 848L, any practical limitations on the number of devices on each trunk, response times, device failure mode(s), fail safe settings etc..

RJ

[Bhavdeep Bhatt]

I am not sure if this is a limitation of 848L or we are missing anything but I will share this with you anyways. May be someone can help us both.
We have been testing 848Ls with our host DCS system for performance. We generate dry relay contact closure and open every second through a timer relay. This way 848L input should see rising trigger every two seconds. The NO contact of timer relay is connected in parallal to channels 1,2,3 and 4 of the 848L. Our DCS tags monitor this open and close condition using DI function blocks every 50ms and count them up at rising trigger. With only 848L on H1 link and macro cycle 250ms, we miss about 10% of pulses on our DCS counter tag. There is a counter right on the 848L per channel. These counters dont match with each other either.
We are still troubleshooting this issue. As we start reading additional channels from the same module we start loosing more pulses upto 90% of pulses are lost.
You can try similar testing with your host system and see how it behaves.

[jdcobb]

Mechanical relays can exhibit a "bounce" on contact closure. The input filter of the 848L will eliminate this effect which is a likely cause of the inconsistent counts.