Groundline employs experts who know a lot about power utility modelling. As part of a PhD thesis one of their employees undertook research into the modelling of wooden power poles. By analysing the acoustic signature which changes depending of the stiffness of the foundation and internal decay of the wooden pole, it is possible to determine the pole condition in a quick and non-destructive manner.
Based on this research a software mathematical model was derived, however with no hardware to undertake the test Groundline turned to Proto Electronics to develop custom hardware to validate the system.
Key features of the system included:
- Two analogue inputs one for the geophone which measured the transmitted impulse energy and the second which connects to a piezo electric hammer to generate the excitation force.
- An easy to read colour screen.
- Automatic logging of the test location through an integrated GPS module.
- Durable high quality Lemo connectors designed to withstand repeated shock impacts seen during the hammer operation.
The solution
Handheld processing unit
Prototronix already had a similar product which had already been developed the TVM1100 tunable voltmeter. One of the first steps in the design process was to see how this product could be easily adapted to meet the requirements of Groundline. The adaption of an existing product had the advantage of reducing the development time, cost and reducing the inherent risk in new product design.
To meet Groundline requirements we added a new power supply for the hammer and created a new software build these changes were retrofitted into the existing TVM product.
PCB Design
The THOR unit single PCB design contained all of the processing components – such as the microprocessor, power supply circuitry, analogue amplifier and LCD screen. Very tight design constraints were placed on the main PCB to ensure it could be easy hand held.
To reduce the size of the PCB (thereby increasing density), we implemented the following techniques:
- Multi layer PCB (6 layer)
- Small surface mount (SMT) components, including a 208 pin microcontroller.
- The use of integrated modules such as GPS and display panels which both uses highly compacted component assemblies.
Digital processing system
The THOR unit made extensive use of digital processing algorithms developed in conjunction with Groundline engineering support. The processing was undertaken by a NXP ARM based microcontroller. The hardware also enhanced the software by using a high performance analogue filter to greatly minimise the interference generated when operating near power lines.
Power Supply Circuitry
As the device was required to be as light as possible – we opted to power the circuitry from a rechargeable Lithium-ion (Li-ion) battery. Li-ion batteries have the highest energy density of all rechargeable batteries.
LCD Display
While there were many possible display screen options, ultimately an LCD screen was chosen. We took extra care during the selection to ensure good readability even in outdoor locations.
Electro-mechanical Integration
We worked very closely with Groundline, who oversaw the testing of the unit. During testing it became apparent that the connections between the handheld unit and the hammer were a weak point in the design. Proto undertook research and was able to source a higher quality cable assembly which resulted in increased durability.
For the PCB, we were able to utilise our in house prototype technician. This resulted minimal tooling costs for Groundline and a rapid turn-around time for their prototype.