Original Article dated: Dec 17, 2008 By: G. Raymond Peacock, Temperatures.com Inc.
During the past year, I’ve been discussing some of the best practices required to successfully add a new sensor to your operations. This month, I’ll examine the next to the last step in the process: commissioning the sensor. In this phase, you’re simply ensuring the sensing device is functioning and will continue to do so for an appropriate length of time.
Covering All the Bases
All too often, this step is overlooked, even though it is a key part of the installation process. The challenge here is that there are no universally accepted guidelines to follow.
So I’ll review seven steps that have served me well over the years. The essential tasks involved in commissioning a sensor can be summarized as follows:
* Ensure the sensor is installed properly, with all its inputs and outputs complete.
* Verify the unit is mounted properly. For example, if you are working with a device such as an imaging camera or infrared thermometer, be sure it’s aimed at and focused on the proper target. When appropriate, make sure the device is connected to the sample and reference taps.
* Ensure the sensor is powered properly (e.g., loop current, 24 VDC, 115 VAC, or 240 VAC) and is delivering the correct signal (e.g., analog current or voltage, digital, correct format, or opto) to the correct device or system.
* Verify support services, such as air purge or cooling, are functioning as needed.
* Be sure installation details and up-to-date manuals and support documentation are readily available for the maintenance staff.
* Make certain the sensor is logged into the control or monitoring system and identified correctly, as specified in the system coding scheme.
* Ensure support personnel understand the equipment, its installation, and maintenance needs and are capable and outfitted properly to maintain the device.
The actual details of each installation depend a great deal on the type of sensor and how it interfaces with the object of measurement and the monitoring or control system to which its output is delivered.
Support Staff
You should demonstrate to those responsible for the device’s routine maintenance just how to check the installation. They may need orientation or special training, especially if the device is new to them.
They may require special tools, test devices, or experience dismounting and remounting the sensor and its accessories. Make sure they know how to diagnose complex faults or misconnected leads should something be changed or destroyed in an accident.
Be sure the support staff is aware of the device’s role in the process under control. Some systems are complex. If a single sensor is changed or mislabeled, the problem can slip through the cracks and produce miles of defective product.
I’ve gone into a plant to review the installation of devices I have specified and found wiring improperly labelled and device control settings set to arbitrary values. The people installing the sensors were simply unfamiliar with the devices and hadn’t been given the necessary training.
That seems to happen more and more when contractors fall behind on project timetables and short cuts are taken.
This doesn’t mean you should discount plant technicians’ experience and knowledge. They understand the peculiarities of the facility’s operation and can help you commission sensors efficiently and effectively.
Take the opportunity to coordinate with them.
One of the most useful things you can do for them is to help set up a maintenance log. The system should include not only details of the device and its supplier but also provide a place to record the initial calibration certificate number and details.
It should also include installation verification data and schedules for recalibration or calibration reverification and recertification.
If you have problems establishing calibration intervals, check the resources at NCSL International and the Integrated Sciences Group recommendations for calibration intervals and available free software.
Both organizations, among others, offer excellent training programs, some geared specifically for plant maintenance staff members.
A serious tester will have a systematic approach to testing that they can hold to any recognized scenario without reluctance. The one I got many moons ago was to document the tests for extracting a can from a lemonade vending machine. I did the entire prerequisites, studied the testing environs, determined the machine was fit for testing and begun the “tests”. Put in too little money, get money refunded, put in proper money, have money repaid etc. Then when I did eventually press vend, the can got stuck instead of falling to the tray. So I employed the “workaround” of swaying the machine with my shoulder. My report concluded that the machine was periodically unfit for purpose unless a physio could also be installed in the building to deal with the multiple painful shoulders that would result from its implementation.