Thanks Dan
Yes it is a 2 wire loop powered device, there are no motors in the area or any other
source of noise, it is a tank on top of a hill, there is a farmhouse nearby but no heavy machinery. the times of the spike appear to be random. I do not have a tight correlation on the source being wind in the area but it is windy now and it is more often now. There is no outside influence that I can see other than possibly wind, which points toward the ground loop fault. there are also some spikes in the downward direction.
I am also inclined to believe it is a noise artifact. I will recommend to the client the cable get replaced with a twisted shielded pair cable. It might be only a twisted cable inside a PVC conduit.
It is analog signal to a analog input to a scada box that reads the analog data and sends it via cell phone text message to the servers.
The power supply is a 24vdc with crowbar and powers another analog device that does not show any abnormal behavior. The loop is +24 from power supply to sub pressure transducer to scada to 0vdc.
Thanks thebard3, since the other signal from the scada box is reasonable, I am not looking at the box at this time, though the oem is looking in the programming to suppress this alarm.
Thanks tugboat, the installation of a different type of sensor is more costly, would put another penetration in the tank. We will stick with the sub pressure transducers.
Here is the past 2 days of graphing.
The different top off points are a normal variation in the control that shuts the valve which is subject to velocity depression in its sensor line. (it is a bug that is lived with). The fact that the top is a curve and not a point is due to the surge reduction method used on this valve as the fill line is miles long and goes through several pressure reduction valves along the way.