Greetings!
I just received my new RS 4D and I’m in the process of learning all about it and how to install it at home.
I don’t seem to be able to find much detail on aligning my RS4D to north. I have located the “N” arrow on the board and I’m assuming I use a compass to ensure the unit is aligned to magnetic north. Is that all there is to it?
regards,
Mark Richardson
Well - true north is not what a compass indicates. It indicates magnetic north, which could be perhaps 12 degrees off. If you are out of doors you can use Google maps to find a landmark due north of you (true north) and use that, There are GPS phone apps too. But I suspect it is not all that critical in any case.
Ken
Thank you. Good information. I understand a compass is indicating magnetic north but is the alignment of the RS 4D supposed to be true north or magnetic north?
regards,
Mark
It has got to be true north … since magnetic north moves position over time … comparing data over the years would be chaos.
The instructions say to use a compass. Of course, there are compasses that have a little ring you can adjust to compensate for declination. They must mean one of those 
@m9richa calculating declination can be tricky if you’ve never done it before. You may find it easier to use some software tool to do it for you, such as NOAA’s here:
https://www.ngdc.noaa.gov/geomag/calculators/mobileDeclination.shtml
I’d argue that it doesn’t actually matter, providing you keep the instrument alignment constant.
The E and N components are orthogonal, so they can easily be transformed to true N and E in the data processing stage.
Oftentimes, it’s easier to apply a correction/offset to an instrument than to precisely position it.
To do the correction you will need to know the actual/precise orientation of your device.
How would you do that? Does a really good shake, from a known direction, contain enough information for you to determine the true orientation of your device?
No, you need to measure the orientation once the instrument is in place, then apply a transformation to get true N and E.
What I’m saying is that this is often more straightforward than trying to manoeuvre the instrument itself.
And the best way to measure the orientation is to use an orienteer’s compass like this:
https://rockclimbing.world/products/silva-expedition-4?gclid=Cj0KCQjwho7rBRDxARIsAJ5nhFoiqf1OGtrm5GHODIfwXDrvYyCDncOBqgc1Z7btW_7aU1QhoYAA7d4aAiiPEALw_wcB
Thanks to all for the feedback. It was all useful in helping me figure out a way forward regarding my RS installation.
I discovered there are several free smart phone apps out there that will help orient me to True North. I’ll use them to align my RS 4D so no need to transform or recalculate the seismometer orientation.
regards,
Mark Richardson