TWO AUXILIARY TOOLS FOR FACILITATING THE CALIBRATION AND
THE EXERCISING OPERATIONS

THE MINICALIBRATOR AND THE EXERCISE SYRINGE

 

THE MINICALIBRATOR

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The Minicalibrator is an auxiliary tool permitting to perform handily the calibration of a membrane (determine DA, DB) and to verify the proper functioning of a blade (regular on/off switching of the signal), without need of deploying the regular control box.

Characteristics of the Minicalibrator:

It is small (20 cm long) and light (200 grams), and is able by itself (without control box, cables, ground cable) to check DA, DB of a blade.
It is equipped with a pressure gage that is small, but has a scale spanning the full tolerance range (-30 to 80 KPa), and therefore is very accurate.
It is equipped with a small buzzer and a battery that will last for years. Uses one 1/2 AA 3V battery, terminating with wires (easily found in computer shops).
It is directly screwed (as a screwdriver) on the rear of the blade.

It fulfills fast and conveniently the following tasks :

Check DA, DB after a blade has just been revised.
Check DA, DB and run a general functioning check of a blade in the office before moving to a site.
Check if DA, DB have reached regular values after installing / exercising a new membrane.
Check handily in a hotel room, after a day of field work, if the blades are working properly. If DA, DB are outside the green scale of the gage, the membrane has to be replaced. (Note that blades older than 1990 may have DA, DB too high. Anyway DA, DB of a new membrane in an old blade can still be reduced within tolerance by interposing an additional 0.15 gasket on top of the basic gasket).
Permits to field supervisors to verify quickly if the blades in use at the site are working properly and DA, DB are in tolerance

"Cleanliness" check

The Minicalibrator also permits to verify if the inside of the blade, below the sensing disk, is free from dirt or pieces of tissue or fabric. For this check, the operator applies 10 or 20 push-pull cycles and note if the signal inversions are sharp. If they are "hesitant", the operator should remove the membrane and clean or blow off dirt from the electrical contact points.

NOTE

DA, DB of a real test, as a rule, must be taken - and written in the data sheet - just before (and after) a sounding using the same control box used for performing the sounding. Hence DA, DB taken previously with the Minicalibrator have to be considered as indicative. Nevertheless, in most cases, the differences are very small.
Due to the lack of tubing, the response of the gage of the Minicalibrator to the pressures applied by the syringe is immediate. This immediate response should not induce the operator to forget that, when he takes DA, DB with the usual 20 or 30 m DMT tubing, there is some time lag, and therefore, in the configuration with real tubings, he must take DA, DB slowly.

 

THE EXERCISE SYRINGE

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The "exercise syringe" is an auxiliary tool permitting to perform handily the exercising operation, without need to use the gas tank, the control box and a tubing.

The exercising operation is performed whenever a new membrane is mounted. The scope is to stabilize DA, DB. The operation consists in pressurizing the blade in free air at 4-5 bar.

The "exercise syringe" is directly screwed (as a screwdriver) on the rear of the blade. Note that the syringe has a START mark and an END mark. Before connecting the syringe to the blade, the piston should be at the START position, then the syringe can be screwed to the blade.

When pushing the piston of the syringe from START to END , the air pressure will reach 4 to 5 bar, which is the pressure needed for the exercising (the force is approximately 25 Kg, or 250 Newton).

The exercising pressure can be applied only once, or, equally well, 2 or 3 times.

If the exercising is performed with the blade vertical submerged in a bucket of water, it is possible to verify blade airtightness.

After exercising, insure that DA, DB are in tolerance : DA=0.05 to 0.30 (typically 0.15), DB= 0.05 to 0.80 bar (typically 0.40).

 

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Last modified: 21 June 2017