Allen-Bradley 1771 relay contact output modules offer dry circuits, that is, circuits without leakage current. Leakage currents are present on solid-state outputs; these currents are capable of energizing highly sensitive output load devices such as low-power latching relays.Allen-Bradley 1771 open contacts on output relays assure that no leakage currents occur in critical applications.
Allen-Bradley1771 relay contact output modules offer either normally-open (Form A) or normally-closed (Form B) configurations. You can select the form configuration for four of the contact output modules, the 1771-OW, -OW16, -OWN, and -OX. The 1771-OW has eight selectable outputs. The 1771-OW16 has eight normally-open and eight selectable outputs. The 1771-OWN has 32 selectable outputs.The 1771-OX has four selectable outputs. Selectable–configuration means you can predetermine whether an output will be on or off when local power is lost to the control system or the output module.The 1771-OWNA has 32 non-selectable normally-open contacts.
Allen-Bradley 1771 relay contact output modules use one of the following relay types:
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Provide output isolation.Isolation helps assure that a failure on one output circuit does not pull down another output circuit, thus increasing overall system integrity. This isolation also protects the backplane logic from line transients on the output circuits.
Increase flexibility in applied voltages.You can apply either ac or dc voltages to relay contact output circuits. The range of these voltages can be broad (within the module’s operating specifications) without impacting the module’s performance. Sink or source power.Contacts on relays permit dc outputs to be sinking or sourcing as required by the devices being controlled. Solid-state outputs require specific compatibility with the load device as to current sinking or sourcing. Switch analog signals through relays.You can use analog module inputs for different devices by switching circuits through relays. Analog signals are typically low voltage (+10V dc) and low current (4-20 mA). Contact resistance can be critical, and should be accounted for in low-impedance circuits.
When using relay contact output modules, you must consider the following:
Relays have a finite number of operations during their life. This varies depending on the current loads and voltages you apply relative to the relay’s design specifications. A relay that is always operating at the same load conditions has a very predicatable life. A low power load delivers longer contact life when the minimum load conditions are met. Varying load conditions can drastically shorten contact life. Do not operate a contact at low current or voltage conditions after operating the same relay under high power conditions. Operate at low power first, then at high power. Electromechanical relays typically have a longer life than dry-reed relays. When selecting a relay type, we recommend that you consider the number of operations expected over time and the load placed on the relay. The switching frequency of a relay is limited by its mechanical characteristics. To obtain maximum relay life, do not exceed the maximum switching frequency of the module.