Convenient broad range pressure calibration
April 2005
Pressure Measurement & Control
Mensor has for years concentrated its activities on delivering accurate automatic pressure controllers to sensor manufacturers such as Rosemount. With the introduction of the new 600 controller/calibrator, Mensor is making a play for the less critical applications; typically end-users who wish to calibrate high performance pressure transmitters.
Consider that at around 4 MPa on air, our National Pressure Standard has an uncertainty of about 45 ppm. This means that any calibrator much better than 100 ppm will need to be sent overseas for certification. Next consider that if a test uncertainty ratio of 3 is used - which is the minimum recommended for good practice - then a 100 ppm FS controller has only a 3,3:1 useful range when calibrating a 0,1% transmitter, which is not so uncommon today. This means that a 1,6 MPa controller can only be used down to 500 kPa. This is not much utility when forking out the best part of six figures. So what is the solution?
Blanes is offering the Mensor 600, with eight pressure ranges in a single instrument. This is achieved in a primary design that packages two regulator channels in a single instrument. Allowing each regulator channel to have two separate transducers provides the second range extension. Giving each transducer two ranges provides the third range extension. The 100-ppm uncertainty now applies to each individual range in the box. A final range extension is provided by an optional barometric reference, which allows absolute emulation of gauge transducers and vice versa. So in a way there are 16 ranges available. There are also two unusual, though not unique features.
1. The low-pressure regulator (0-100 kPa) has a built-in pressure generation capacity, so no external pressure source is required.
2. There are no mechanical switches in the instrument, except for power switch. All settings are done through a full-colour multilingual touch screen.
Using the example above, a low-pressure controller may be configured to give complete coverage from 100 kPa down to less than 200 mm wg. If transmitter accuracies are only 0,25%, the range can be extended down to close on 30 mm wg. This performance is achieved by characterising the best sensors on the market and storing the calibration data in the transducer in digital form for dynamic compensation. The controller is capable of full remote control over an Ethernet connection, and can be automated using a suitable software package and compatible DMM.
Transducer modules can be removed for calibration or service. Since the calibration configuration data is stored on each transducer module, swapping one transducer with another of the same, or different range is possible. So on-the-shelf spare modules can be interchanged with modules in the Series 600 to virtually eliminate downtime during calibration cycles.
Further reading:
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