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Grade changes when I turn around

JOHN140

Active Member
Joined
Oct 21, 2012
Messages
42
Location
LUBBOCK, TX
I’m using Trimble gnss on a 140m. Dual mast cb460 all the normal 2d sensors and a pitch sensor. Machine grades perfect going one direction but when I turn around and go over the previous pass in opposite direction blade is .10sh high consistently. GPS vertical error was .03 and pdop 1.3 the other day when this was going on. What would cause this. Any help is greatly appreciated.
 

Shimmy1

Senior Member
Joined
Aug 14, 2014
Messages
4,257
Location
North Dakota
Is this a new problem? I use Outback RTK for surface drainage on a scraper, and varying grade like this is pretty much normal. My total system only cost about $20k, and being off a tenth really doesn't matter much to a dirt ditch with a foot of drop in a half mile.
 

Tones

Senior Member
Joined
Mar 15, 2009
Messages
3,059
Location
Ubique
Occupation
Ex land clearing contractor, part-time retired
From what you describe seems like a problem with the compass. I've seen it with Topcon on a single mast. But I'm only guessing.
 

JOHN140

Active Member
Joined
Oct 21, 2012
Messages
42
Location
LUBBOCK, TX
No it’s not a new problem, been happening probably ever since system was new. Sitech has always thought it was something to do with 2d sensor calibration but recalibration seems to have no affect. Grade is very consistent when it’s missing. Will stay the same height off the first pass for the entire second pass. Seems there has to be something you could do to bring them together.
 

Gradechecker

Member
Joined
Apr 18, 2021
Messages
19
Location
Michigan
Are you selecting one side of the blade ? How many satellites do you receive ? Sitech is pretty good about fixing bugs like this
 

skyking1

Senior Member
Joined
Nov 3, 2020
Messages
7,462
Location
washington
I know nothing, but is the sensor position offset from the blade edge in the longitudinal dimension? Logical me would think, if the sensor is not really close to over the top of the blade edge this could happen.
 

Gradechecker

Member
Joined
Apr 18, 2021
Messages
19
Location
Michigan
You could play with your vertical offset on the second pass to get it closer but shouldn’t have to strange I’ll ask my operators tomorrow if they have had this happen before
 
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