INFORMATION SERIES
 

UNEXPLAINED DIFFERENCES

20190305

A mystery worth solving is why two devices, in the same room, and armed with the same sensors, react differently. Good examples are Node 3 at Merrimack, NH with the new I1.22RBU and Node 5, also with the same sensor board. Node 5 has coords for Goffstown but that is just to separate the registration dots. On March 4th, after the limits had been lowered from 30 to 20, Node 3 had triggered an alert. Since the alarm didn't stick in alert mode it is considered as a potential valid "hit". After the event I went in and raised the limits to 25. Below is the screenprint showing a compass heading change of only 1 degree. What triggered Node 3 was a temporary 10 mGa increase in background.

Node Id Event Type Compass (deg) mGa Avg. Ambient mGa Pressure (in/Hg) Date Time
3 alertStart 150 20 988.84 30 2019-03-04 20:31:19
3 status 149 10 988.84 29.53 2019-03-04 20:31:17

20:31:19 is 1500 hours 31 min 19 seconds, or 3:31 PM.

Upon checking Node 5, in the same room, it was discovered that there was no data on the spreadsheet since that device was not triggered. However, the limits setting (also referred to as trigger) is set at 20 as well. I didn't raise this node to 25 because it didn't activate. The question now is how low do we have to take it before it records a hit at the same time Node 3 goes in alert? For the test I lowered it 5 mGa to 15. Let's see what happens.

The important thing is there is a reason for this, and most probably the temporal location. It's the same room but just what is nearby Node 5 that is masking the hit or why is Node 3's position making it more sensitive?

I am suggesting to Paul A. (who runs these two nodes) after a day or two to simply switch the nodes in their exact identicle positions so that the local E-M background will be duplicated but using different DataProbes. I strongly believe that it is their locations that are at work here and that switching them may give us the answer. If this is done, the limits should be both set to 20 for a while, then lowered to 15.

Two days later at
15:11:01, 10:11 AM & 22:17:54, 5:18 PM
node 5 was triggered, but node 3 was not.

Node Id Event Type Compass (deg) mGa Avg. Ambient mGa Pressure (in/Hg) Date Time
5 alertStart 138 22 880.22 30 2019-03-06 22:17:54
5 status 134 3 880.22 29.88 2019-03-06 22:17:07
5 alertStart 138 17 886.83 30 2019-03-06 15:11:01
5 status 135 2 886.83 29.84 2019-03-06 15:10:17

Both nodes are now set at 20. I'm suggesting we test these nodes
1) separated
2) switched positions
3) both at position "A", then both at position "B".

I wish that the spreadsheets included the trigger numbers since it is difficult to monitor these nodes without taking notes.

Much of the beta testing by our software team in the past has been conducted with a new device and an old device, but we are now also testing with all new sensors.

Fran Ridge
MADAR Director