Release Date: 16 June 2009 |
Survey
S Series Total Stations: J and N Constants for PPM Calculation
Products
- S Series total stations
- Trimble® VX™ Spatial Station
- Trimble Survey Controller™ software
Question
Where can I find the J and N constants that I need to compute the PPM corrections for different instruments?
Answer
The Trimble Survey Controller Help (available as a pdf file on the Trimble Survey Controller Installation CD) includes the formula to calculate the PPM value atmospheric corrections.
This formula has two constants, J and N. A table provided with this formula shows the values of these constants for a range of instruments. For the Trimble VX Spatial Station and the S Series total stations, the J and N constants values come from the instrument.
These values are shown in the Job Xml export file:
| Total station | Values |
VX S6 DR300+ |
<Type>TrimbleVXandSSeries</Type> <RefractiveIndex>273.9420092103</RefractiveIndex> <CarrierWavelength>79.255958549223</CarrierWavelength> <Model>VX</Model> |
| S8 HP | <Type>TrimbleVXandSSeries</Type> <RefractiveIndex>278.77885604639</RefractiveIndex> <CarrierWavelength>80.655338415988</CarrierWavelength> <Model>S8 HP</Model> |
The values are also available in the DC file, under the Instrument heading or in the text file:
| Total station | Values |
VX |
E4NMVX & S Series 10123 R10.0.58 3 273.942009210302 105.6746113989640 |
| S8 | E4NMVX & S Series 56789 R11.0.76 3 278.778856046393 107.540451221318 |
However, the N constant (CarrierWavelength) given here is for the pressure applied in mm mercury (mmHg) and therefore is 33% higher.
Note: You can safely use the formula from the manual and the values from the DC file. Be aware that the values in the DC file are for pressure given in mmHg, which might not be the actual case. When you process the PPM value from the given pressure value, always check the unit value shown in the header position 43.
