183 Plains Road, Milford, CT 06461
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Thursday, May 23, 2013
Frequently Asked Questions
Normally, a pressure switch is utilized to provide a signal of either an unacceptable increase, decrease or fluctuation in a given system pressure. If only one side, i.e. "increase" or "decrease" in system pressure is important for notification to a computer or operator, do not out a tolerance on the reset value. This results in the technician being required to calibrate both the setpoint and the reset point, requiring additional time and sometimes a custom spring, resulting in additional cost.
In specifying the setpoint tolerance the proper system operation should be the deciding factor. Very often the setpoint of the pressure switch will be specified within a narrow "band" which is unnecessary to provide a general warning system pressure increase or decrease. If the narrow deadband is not required for system operation, Spectrum will advise as to the optimum tolerance, resulting in labor efficiency and therefore less cost.
In general, the cost of the electrical connector, if required, can be a major factor in the resulting price of the pressure switch. Often the customer will require the use of a connector to an applicable MIL-SPEC or QPL (Qualified Product Listing) in which case, there is no option, but in other applications, the use of a commercial equivalent connector can sometimes reduce the cost of the pressure switch assembly significantly at no risk to installation, quality or operation.
A Very common problem in pressure switches with recent years relates to elevated resistance within the unit, emanating from the electrical microswitch contacts. In the past, aircraft (or other) electrical systems operated on 28 Vdc with 1-3 amp current. This electrical current was sufficient to "burn off" any minor corrosion or contamination which might inhibit the proper actuation of the microswitch and therefore the pressure switch. With the advent and proliferation of flight computers, the electrical current was reduce significantly (from amps to mili- or micro-amps) and in many cases, existing specifications or drawings as the component level have yet to be revise to reflect this change. Spectrum provides pressure switches with either gold- or tim-plated electrical contacts, dependent upon the specifications. In general, if an application specifies 100 milliamps or less, gold-plated contacts are provided for optimum continuity. Correct identification of the electrical characteristics of the system is paramount for best reliability.
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