Relays Models 681 Nullmatic Biasing Relays Introduction Features & Benefits Precision relay with a small form factor provides OEMs with mounting flexibility Powder coating provides improved corrosion resistance Description The Model 681 Biasing Relay is a Nullmatic regulator with plus and minus bias adjustment. It operates on the Nullmatic principle, which holds the output pressure constant regardless of wide changes in flow or supply pressure. The Model 681 Biasing Relays are often used in control circuits where a single pneumatic signal operates more than one final control element in parallel. The plus and minus bias adjust the respective loads. The Model 681 is air-loaded by an external signal. Its output is maintained higher than the external signal, equal to it, or lower than it by the amount of the manually-set bias. Mounting Dimensions Specifications Normal Input Range 3-15 psig Bias Adjustment +18 to -14 psig Supply Pressure Normal: 20 psig Minimum: 2.2 psig greater than max. output pressure Maximum: 150 psig Maximum Input Pressure 100 psig Minimum Output Pressure 7 0.02 psig Air Consumption 0.07 scfm at 3 psig output with 20 psig supply Ambient Temperature Limit -40 to 180°F (-40 to 82°C) 7.39