In the field of utility locating, selecting the appropriate frequency is crucial for accurately detecting and tracing underground utilities. Active frequencies, which involve using a signal transmitter like the DA300 to apply a dedicated signal to a utility, offer different advantages and challenges depending on the specific frequency used. Unfortunately, no single frequency is universally effective for all locates. This paper explores the key active frequencies in greater detail to help clarify their applications.
Low Frequencies: 512 Hz and 640 Hz
Overview:
512 Hz and 640 Hz are considered low frequencies in the context of utility locating. Due to their low energy levels, these frequencies do not easily couple to utility lines that are in close proximity to one another.
Application:
These frequencies are typically used in connection mode because their signal strength is insufficient for induction. And are perfect for tracing cables over longer distances, another common use case is in sewer inspection cameras, where these frequencies help track the location of the camera within the pipeline.
Limitations:
While effective in specific scenarios, such as tracking sewer inspection equipment, these low frequencies are not suitable for general-purpose locating due to their limited coupling ability and reliance on direct connection.
Medium Frequencies: 8 kHz and 33 kHz
8 kHz Frequency:
Overview:
The 8 kHz frequency is categorized as a medium frequency and is one of the most versatile options available for utility locating. It strikes a balance between being high enough for both induction and connection modes while maintaining a relatively low tendency to couple with unintended utilities.
Application:
This frequency is especially useful when locating larger diameter utilities, where other frequencies might either over-penetrate or fail to couple effectively.
Limitations:
Despite its versatility, 8 kHz may not be sufficient for locating small-diameter utilities, where a higher frequency might be necessary for adequate signal propagation.
33 kHz Frequency:
Overview:
33 kHz is another medium frequency, often regarded as the industry standard for utility avoidance work. It provides a good balance between inductive and connective coupling, making it highly adaptable to a variety of locating scenarios.
Application:
This frequency is frequently used for both short-range and mid-range locating tasks, offering improved coupling with smaller diameter utilities compared to 8 kHz.
Limitations:
One downside to 33 kHz is its higher propensity to couple with unintended utilities, which can lead to signal interference and less accurate locates.
High Frequencies: 83 kHz and 131 kHz
83 kHz Frequency:
Overview:
The 83 kHz frequency falls into the medium-to-high range and is typically employed in challenging environments, particularly where soil conditions are dry and sandy. Its higher frequency allows for better penetration in these difficult conditions.
Application:
83 kHz is particularly useful for locating utilities in environments where lower frequencies might struggle due to poor conductivity or challenging soil types.
Limitations:
However, this frequency tends to couple more easily with unintended lines, and its signal strength diminishes over longer distances, making it less effective for extensive locates.
131 kHz Frequency:
Overview:
At 131 kHz, this is the highest frequency available on the DA300 and is generally classified as a high frequency in utility locating.
Application:
This frequency is ideal for short cable runs and small-diameter lines where other frequencies might fail to couple effectively.
Limitations:
While 131 kHz provides excellent coupling for specific applications, it has limited range and is not suitable for long-distance locates. Additionally, it can couple too easily with unintended utilities, leading to potential misidentification.
Conclusion
Selecting the right frequency for utility locating requires a thorough understanding of the environment and the specific characteristics of the utilities being traced. Each frequency has its strengths and weaknesses, and the choice of frequency should be guided by the specific requirements of the locate, such as the type of utility, the surrounding environment, and the desired range. By understanding these factors, operators can make more informed decisions, improving the accuracy and efficiency of their locating efforts.
