Ratings (Hysteresis)

The tradeoff in selecting a higher power reed is a greater hysteresis and reduced switch adjustability.

Hysteresis is  =  (Switch On Inc. – Switch off Dec.) / Full Scale range   Stated in % of Full Scale Range(FSR).

For example the average Hysteresis of the 3W SPDT switch for Mid-West Instrument Model 120 is 5%, whereas the 60W SPDT switch is 13 %.  In most applications (ie; pressure drop across a filter), hysteresis is not a parameter to be concerned with.  However, large hysteresis limits the ability to set a switch near the bottom of the range.  In some cases a switch can be set on increasing pressure below the defined capability; however it does not clear when the differential pressure drops to 0.

Hysteresis on a DP switch is actually a good feature to have.  The switch Hysteresis provides a mechanical filter to prevent a constant oscillation or cycling of the switch around the set point.  Unfortunately, for reed switches the hysteresis cannot be adjusted and will vary from unit to unit.  Note that our specification specifies a nominal and maximum value.

Switch Specification Hysteresis

ModelSPST (60W)SPDT (60W)SPDT (3W)SPST (25W)
Model 12015% / 8%(F.S.)20% / 13%(F.S.)10% / 5%(F.S.)N/A
Model 12118% / 10%(F.S.)N/A12% / 8% (F.S.)N/A
Model 130N/AN/A10% / 5% (F.S.)N/A
Model 140/142N/AN/A10% / 5%(F.S.)15% / 8%(F.S.)
Model 22020% / 10% (F.S.)20% / 18% (F.S.)10% / 6% (F.S.)N/A
Model 24020% / 9% (F.S.)25% / 18% (F.S.)15% / 6% (F.S.)N/A
Model 52228%/18% (F.S.)N/A23%/16%N/A