IR: What's a survey? What's a route?

Ray Garvey

This is the first in a series of articles addressing the application of modern infrared cameras to in-plant thermography. This particular article answers the question "What is the difference between a survey and a route?"

Routes were first introduced into plant thermographic inspection procedures in 1993. Route-based data collection is commonly used for walkaround vibration analysis, preventive maintenance inspections and other step-by-step procedures. This sequential process is intended to collect thermal information by periodically inspecting the same point on an equipment or machinery asset. An underlying database is used to track and trend problems and corrective actions. The in-field inspection system includes equipment information and fault tree logic that prompts the thermographer through a process. The result is a fully documented inspection with automatic reporting.

Many infrared thermographers are inclined to use a survey-based inspection approach instead of, or in addition to, a route-based program. Surveys, like routes, may be sequential, but not necessarily. In a survey, you normally walk up to an area and inspect around that area. So, a survey is most often the process of inspecting the vicinity.

Let me use an everyday example to demonstrate the differences between surveys and routes. My wife is a route-based shopper; whereas, I am a survey-based shopper. Before she goes shopping, my wife draws up a shopping list. She notes a shopping item in the middle of the page, then one on the top quarter, and another on the end of the list-in-progress. She knows the order that products will be seen as she walks the aisles of a favorite store, and she puts things listed in order by where they will be found on the shelves. Since she shops frequently at the same store, this process is very efficient. It allows her to gather just the items she needs and avoid impulse buying. The process keeps her coming back to the same store, even if it means driving past others that are laid-out differently. If she hands me her list and sends me off to shop, I will say, "thank you very much," and find it easy to follow.

However, if it's up to me to write out the list, there is absolutely no way I could organize the route-based shopping list. I don't know, and will never know, the organization of the store. I don't enter the same store often enough. Everything gets moved around. So, what I employ is a survey-based shopping method. I make a list of the things I want to consider buying and look in my wallet to know my spending limit. I then go through the doors of a preferred store and read the signs. Some signs hang from the ceiling or at the ends of aisles. Some signs are in the form of a store or shopping mall layout. Other signs are more intuitive, considering customary ways that store owners group things together.

The system I follow is a survey. To do a survey, I enter an area where I expect to find an item of interest, and then I inspect that area. By the way, the store owners know this tendency many shoppers have to "survey," so they put stuff out that will grab the attention of impulse buyers.

What does this have to do with thermographic inspections? I find that thermographers generally prefer to use the survey-based method. That means a thermographer selects an area, such as a switchyard, and walks through the area looking for things. It's not a point-by-point thing; the thermographer covers much new ground each year. Vibration routes are walked every month, whereas infrared surveys are far less frequent and far less point specific. Then the surveying thermographer has a defined list of tasks that must be performed or inspected during the survey of an area.

Some people mix route and survey methods together. An advantage of this is that routes provide records of all things inspected, normal and unusual. Surveys tend to be more exception-based, although this is not always the case.

Infrared thermographers have always done surveys, so what's new? The new thing is the use of survey templates to assist with the inspection. Figure 1 shows four different kinds of survey templates that can be programmed into computerized infrared camera systems:

  • Sequence of inspection requirements

  • May prompt visual inspection or photo

  • May prompt "Warning!"

  • Physical layout in the vicinity of the area to be inspected

  • Task checklist

  • Location of a component within a system

    Figure 1. Four kinds of survey templates prompt
    the infrared inspector.

    All modern infrared imaging systems have imbedded computers driving graphical displays. There are a number of things that this display can be used for to prompt the operator through the inspection process.

    Survey templates may include things like a plant-floor layout, an aerial photograph, an annotated diagram or a photograph of equipment to be inspected. For example, Figure 2 is a line drawing showing components, transmission lines, and connections surrounding a particular transformer and circuit breaker. With this information in hand, the infrared thermographer is better able to perform the inspection and to fully interpret the nature and consequence of problems detected.

    Figure 2. This line drawing shows components, lines and
    connections surrounding a transformer and circuit breaker.

    One major advantage for using survey templates is the way this helps standardize a process that is going to be used by several people or for use in a variety of areas. Here are three other tips to assist inspectors in performing efficient, effective and safe infrared surveys.

  • Get trained and certified.

  • Document your findings for easy reporting and follow-up.

  • Carry tags in your pocket; mark things found so others can come back to the same exact location.

    In summary, routes are sequential, measurement point to measurement point. They provide an easy way to annotate every item inspected, whether or not any findings are noted. They are best suited for regular, monthly inspections. Surveys are conducive to inspecting an area; they do not necessarily have to be point-to-point. Survey templates can be used to navigate a thermographer through an inspection process. Templates can be a high-level view of the plant, a close-up perspective of an equipment system or a series of prompts to help the infrared inspector do the survey correctly.

    Ray Garvey is an engineer with Emerson Process Management’s Asset Optimization division. Contact him at 865-675-2400, ext. 3435, or


    Piety, et al, U.S. Patent 5,386,117, "Infrared Thermography System Including Mobile Unit."

    Garvey, et al, U.S. Patent Application SN 10/872,041, "Method of Automating a Thermographic Inspection Process."

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