The power anomalies that can cause problems in the laboratory are:
Intermittent power as well as improper voltage, frequencies, grounding and wiring are types of power anomalies that can cause problems in the laboratory. Many of these conditions overlap and can occur simultaneously. This is a brief discussion of each of these conditions and what specific problems they cause in the laboratory.
This information is drawn from discussions with lab techs in several countries, as well as meetings with the laboratory equipment repair personnel in Zambia and Haiti.
It is commonplace for developing country grid power to experience frequent outages. This is often the result of load shedding resulting from chronic generation capacity shortfalls or service outages resulting from failure of specific generation, transmission, or distribution equipment. Power outages can be scheduled or random, and can last for a few seconds to months.
If no back-up power supply exists for the laboratory, all automated tests stop when the power goes out. If power cuts are frequent and prolonged, these delays can severely impede the workflow of the laboratory and complicate diagnosis and treatment.
Power outages can also be a problem for the accuracy of some laboratory infrastructure. For instance, one model of the CD4 machine has an internal clock that, at a pre-programmed time, goes into a cleaning cycle. This is most often done during night time hours, and requires that power is present so it can “turn itself on” and go through the cleaning cycle. When the power is disconnected from the lab, this cleaning cycle does not take place, compromising the validity of test results.
Extended power outages also complicate storage of cold-chain dependent reagents and blood.
Laboratory equipment is designed to work at a certain voltage (e.g. 230VAC) with a tolerance range of 5% or 10%.
Most equipment manages fairly well in voltage ranges of plus or minus 10% of nominal design voltage.
However, it is not uncommon in many locations to see voltage sags of much more than 10%. Different equipment performs differently at abnormally low voltages.
Equipment with motors and compressors will tend to wear out much sooner when they are continuously faced with operating at low voltages. Equipment associated with computers, or with computer – like power supplies, will also experience a high failure rate at low voltages. The efficiency of refrigerators is also significantly compromised at low voltages.
Some test equipment, such as many CD4 models, will give the lab technician a report that the test failed due to low voltage, and the test would need to be repeated.
Besides voltage sags, there are voltage spikes. Voltage sags are usually low voltages that last for an extended period of time. But, voltage spikes are extremely high voltages that come through the lines momentarily for a variety of reasons. Often these can be caused by the grid or a generator being abruptly disconnected without warning. Voltage spikes will cause problems to all sensitive electronic equipment, including CD4 machines, blood chemistry machines, and hematology machines.
Like voltage tolerances, different pieces of equipment have different sensitivities to “out of spec” frequencies.
Biomedical Engineers in several countries have reported frequency variations to be especially problematic for any equipment which relies on lasers, such as the CD4 machines. When frequencies get too far out of range, the tests results are affected and the equipment can be damaged.
Low frequencies can be caused by a power generation problem with the national grid. But more likely, a low frequency problem is caused by a generator that has not been maintained and is running slower than it should be, thus putting out a low frequency power supply.
The concept of the ground wire is fairly recent, and in many developing country health facilities it is not installed. (Even where the receptacle has three prongs, there is often no ground wire installed.)
The common problems with the installation of the wiring are that (a) the hot and neutral wires are reversed, (b) there is no ground wire, and (c) the ground wire is not connected properly at the main service. Until the advent of sensitive electronic equipment these wiring details did not cause many problems. But now, much of the equipment depends on the proper orientation of the hot and neutral conductors, as well as the proper existence and connection of the ground conductor.
All of the equipment suppliers interviewed stressed that proper grounding was important for proper equipment operation. Some equipment depends on the proper wiring to use voltage reference points, which it then uses to calibrate and control its tests.
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Last updated: September 28, 2011
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