The problems and challenges of calibration amidst less than ideal ambient conditions.

SEVERAL CHALLENGES FACE THOSE RESPONSIBLE for calibrating pressure sensors for critical air environments, including pharmaceutical plants. Pressurization equipment requires highly accurate calibrations to certify that pressuresensors are working correctly.

Unfortunately, most calibrators used today are bulky, inaccurate, and expensive. Testing crews drag multiple components (a pressure indicator, a pressure generator, voltage and current meters, and the data logger) to test sites, where they are plagued with ambient pneumatic disturbances which can corrupt the differential pressure readings. Crews are also forced to record their measurements by hand on clipboards. These tests waste valuable technician time, with each calibration taking up to one hour, and they open a wide margin of error with so many different components and the manual process of having a technician record numbers ona chart.

In a pharmaceutical plant, for example, rooms may be full of pipes and ductwork, and some of the pressure sensors will doubtless be located in hard-to-reach places. The testing device, therefore, must be able to be transported up a ladder and into cramped spaces, and therefore needs to be small and lightweight. Typically, though, testers find themselves climbing ladders with three or four different pieces of equipment, trying to balance them all as they perform thesensitive tests and then, the task of manually recording the data.

A solution to this problem is for a single, small, and lightweight unit to conduct all of the testing. This all-in-one unit should have an accurate pressure reading device, an accurate pressure generating device, and a computerized test sequence with a meter to read the output from the pressure sensors. The unit should also be automated so that results are automatically uploaded to the laboratory’snetwork, thus avoiding the cumbersome and often erroneous task of manual entry. The ideal calibration equipment is deployable, battery powered, and small enough for one person to carry comfortably, even up a ladder or scaffolding. In short, it must be able to go anywhere and perform the work of several different pieces of equipment. Single-unit calibration testing is a better choice thansystems comprised of multiple components for these reasons.

Figure 1: The testing device must be able to be transported up a ladder
andinto cramped spaces, and therefore needs to be small and lightweight.

Another challenge facing testers using multiple components is the detrimental effect ambient noises have on very low pressures readings. The pressure sensors have two fittings on them, a high side and a low side. To test the pressure, crews compare the pressure in one room to the pressure in an adjacent room. The pressure in the adjacent room is on one side of the pressure diaphragm, and can either be on the high or the low side, depending on whether it is positiveor negative pressure.