What is the accuracy of the PLT 300 and how can I ensure it stays accurate?

Disclaimer: for official accuracy information, please see the operations manual. Accuracy of layout and measurements is strongly determined by end-user competence and understanding of the tool.

Accuracy Specifications for the PLT 300 - Explained

The PLT 300 has millimeter-level accuracy at 50m. Several factors need to be considered when answering accuracy questions, which this article will address. For a quick answer on accuracy, note the following points:

• At a distance of 50m (164 ft.), the PLT 300 has a distance accuracy error of +/-3mm (1/8 in.)

• Errors are tested under ISO 17123-5, meaning they’re consistent and traceable.

• The PLT 300 uses an automatic tilt compensation method to ensure the tool is consistently leveled throughout layout.

  • The tool will mathematically compensate for small residual tilt, but if the tool is significantly out of level, the end user will need to manually re-level the tripod or surface the PLT is resting on.

• The Hilti Construction Layout software is intuitive and flags inconsistencies in measurements for the end-user, as well as provides visual cues to guide corrections.

Relying just on the tool accuracy specifications is not enough to maintain accuracy in layout applications, however, as jobsite conditions and end-user competence also can affect how the tool performs. Therefore, this article will discuss end-user strategies to help keep the tool accurate and mitigate potential errors. 

When should I consider longer range tools?

For longer-range projects and larger jobsites, the PLT 400 is likely the tool of choice. You can see the accuracy documentation here. The PLT 300 is ideal for projects that are within a 50m working radius.

How can the PLT 300 be an accurate solution, even with internal fixed errors?

Errors are almost a given, regardless what kind of layout work is performed. Nothing is perfect. The benefit of a total station is that the errors are known, the errors are consistent, and the errors are manageable.

This means that end users can completely prepare for them, and can understand their implications in their own work. Total station errors can be accounted for, while traditional layout or measuring methods have much more room for error and inconsistency.

With the PLT 300 and other Hilti layout tools, the Hilti Construction Layout software is intuitive, making the operation of total stations less intimidating and easier to understand.

What factors could affect the total station accuracy?

While the tool itself is a very accurate tool for general jobsite layout, care must be taken by the end user to keep it accurate. Important action steps to maintain accuracy are listed below:

Before Starting Work

1. Acclimate the instrument to the ambient temperature (especially after transport/storage) - give it time to sit in the environment you intend to work in before use so the internal temperature is acclimated to ambient conditions. See  the following links for more information regarding weather impact for total stations: weather acclimation and working in wet or dusty conditions.

2. Perform a field calibration before work - Field calibrations are critical to maintaining accuracy.  Have an easy set up on the jobsite to perform these quickly and efficiently with the PLT 300.

3. Inspect the optics/lenses - make sure the main telescope lens itself is cleaned of water and debris. If you see fog inside of the lens, giving time for the tool to acclimate to the outside temperature should eventually see the fog disappear.

4. Secure the total station to not be influenced by jobsite vibrations and movements - jobsites are usually very active,  and care should be taken to protect the total station from being affected by  the traffic or vibrations of jobsite activity. See this article for help regarding securing a total station properly to the jobsite.

5. Have a versatile distribution of control points for stationing - stationing is critical for a total station to conduct layout and measuring applications accurately. See this introduction article to stationing topics, and this article related to control point best practices for more information.

6. Calibrate or check the prism pole - the prism pole must be level when being used for layout to stay accurate.  Verify that the bubbling level provided on the pole is reading accurately, and adjust the bubbling leveling screws if needed.

During Use

7. Regularly conduct backsight checks - checking established control points regularly even after you have set up the tool will help you verify if your accuracy is consistent. See this article, specifically, regarding the  backsight checks  application. This is especially important if you have just moved the tool to a new location.

8. Regularly allow the tool to conduct field calibrations - as mentioned above.

9. Monitor weather conditions - be willing to pause layout if the weather conditions are not ideal for accuracy requirements (wind, vibrations, rain, snow, dust, etc.).

10. Keep prisms clean and scratch free to ensure they are being properly targeted - using a cloth to simply clean dirty prisms could help ensure the total station is finding the center accurately and making accurate measurements.

11. Choose the correct prism type for the layout or stationing you are conducting - sometimes the simplest of mistakes can cause measurement errors. When using HCL, make sure the targets you are measuring to are also correctly indicated within the software.

12. Mark your points cleanly - a total station may be able to measure and guide accurately to a point, but if the marking process is clumsy or inconsistent, the accuracy will diminish simply because of how the points are eventually marked by the end user.

After Use

13. Clean and inspect - Wipe down the instrument, especially of dust and water. Storing the tool in a dry case is important to prevent the humidity of the case environment to allow fog to collect inside the telescope of the tool. In addition, having dust caked on the outside of the telescope could lead to scratches. Anything inhibiting the telescope could lead to inaccuracies.

14. Store the tool at room temperature and in dry places - Avoid storing the tool, especially long term, in extreme temperature conditions. This protects the internal components like sensors and optics from expanding or contracting. It also helps to prevent condensation from building up in the lens, as moving the tool from a freezing (or near freezing) environment to one that is very warm, for instance, could cause internal condensation.

Remember, consistent checks of your work area need to occur to maintain an optimal work environment for digital layout. Control points might get bumped, hidden, or knocked down, dust or fog may be heavy that is affecting measurement readings, weather temperature and barometer readings may be input incorrectly in the tablet, an end user might forget to regularly perform backsight checks to ensure consistency in layout, etc.

While the tool is very accurate, diligence by end users is required.