Campbell Scientific Sentek TriSCAN® Manual v 1.2a - Manual (Page 35)

TriSCAN Manual Version 1.2a
Copyright © 1991 – 2004 Sentek Pty Ltd All rights reserved Page 28
Access Tube and Probe Installation
The information provided below is a summary only. Further information is provided in the Access Tube
Installation Guide Version 1.0. It is recommended that the probes be installed by a trained Sentek
installation specialist.
The aim of the installation is to cause minimum disturbance to the crop and soil profile. Disturbances to the
soil may produce pockets of air or loosely packed soil material. These conditions will cause preferential flow
of irrigation water or rain to a greater depth compared with the rest of the field. Access tubes must be
installed to fit tightly in the soil along their entire length.
Permanent errors can be introduced into the measurements through poor or hasty installations. Air gaps
existing between the sensors (or access tubes) and the soil will bias sensor readings, i.e. the sensor will
read high when the air gaps are filled with water and low when they drain. Poor installation is a primary
source of inconsistencies between sensors.
The additional time taken in careful installation ensures access to accurate and meaningful data. Sentek has
developed precision installation tools to be used for the installation of Sentek access tubes. The precision of
the access tubes and tools is designed to complement the high value of the readings taken by the Sentek
sensors.
Standard TriSCAN Access Tube Installation Method
The standard manual installation method is recommended for most soil types. In this method the access
tube hole is hand augered into the soil, through and slightly ahead of the access tube. This is done using
the 47.0 mm Regular Auger. The augered hole is slightly smaller than the access tube. The access tube is
fitted with a cutting edge that cuts the last of the soil away, providing a tight fit down the length of the access
tube.
This method prevents the formation of air pockets along the length of the access tube and causes minimum
disturbance to the surrounding soil profile. This installation method is proven to be reliable.
Installing the Access Tube
To install an access tube, follow these steps:
1. Put on gloves
2. Put on safety goggles
3. Select the 47.0 mm regular auger head
4. Select the required extension rods and screw the auger head and the T-handle to the extension
rods. The length of assembled auger must exceed the length of access tube by at least 20 cm.
5. Insert the auger into the access tube while the tube is lying on the ground until the auger head
protrudes by 20 cm.
6. Use a marking pen to mark the auger extension rod at the point where it disappears into the top of
the access tube.
7. Remove the auger from the tube.
8. Select the yellow cutting edge and push it into the end of the access tube ensuring it fits squarely.
Note: If you experience difficulties fitting the cutting edge onto the tube then turn the cutting edge on
its side and, with a twisting motion, shave a layer of PVC from the lip of the access tube. Partially fit
the cutting edge into the end of the access tube, then gently bounce the access tube and cutting
edge on the side of the sledgehammer head until the cutting edge fits squarely.
9. Insert the access tube with fitted cutting edge into the tripod guide tube.
10. Select dolly No. 1 or dolly No. 2 and insert into the top of the access tube.