Greetings.

I am using an Emerson meter with an attached Altus net oil computer (NOC) to test the output of oil wells. I have six sites that will be running identical PLC code and configuration. Four of these sites are currently operational. For the most part, 75% of the time, the tests run as they should and the data retrieved is within a norm for that well. The other 25% of the time the data from a previous test remains in the registers. This problem starts without provocation and clears itself without operator intervention. Also, the data that the NOC displays (read by the PLC using MODBUS) for a bad test is not the data recorded in the NOC history registers. Any ideas?

 

Probably a timing issue, as in a race condition, associated with a fast communications connection. The slaves product literature should tell you what the last parameter to be posted of the last test then your host application should trigger on a change in this last parameter.