Contemporary-control-systems BAScontrol20 User Manual Instrukcja Użytkownika Pobierz pdf (Strona 21)

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4.8 Binary Inputs

To sense the action of a push-button or relay, the contacts must have no applied

energy, and be rated for low-voltage, low-current switching. The BASC20 provides

the energy to be sensed. With a web browser, access the Main Screen, click the title

link of any channel UI1–UI8. Set the Channel Type to Binary Input and the Units to

NO_UNITS. As shown in Figure 10, connect the contacts between points A and C.

For common mechanical contacts, polarity is not an issue. The open-circuit voltage

is 12 VDC and the short-circuit current is 0.5 mA.

For solid-state switch sensing, we recommend that an attached solid-state device

have an opto-isolated open-collector NPN transistor output stage with a collector-

emitter output voltage (Vce) of at least 30 V. Output sinking current should be

greater than 5 mA. The collector-emitter saturation voltage should be less than 0.2

V when sinking 2 mA. The emitter must be connected to point C and the collector to

point A (the more positive point). The BASC20 sets the low-threshold to 3 V and the

high-threshold to 6 V. When a contact is made or the solid-state switch is on (resulting

in a saturated output), the voltage at point A is close to zero volts. The corresponding

LED for that channel will be on. If the contact is opened or the solid-state switch is

turned off, the voltage at point C quickly rises towards 12 V. Once the voltage

passes the 6 V high-threshold, the “off” state is sensed. To return to the “on” state,

this voltage must fall below 3 V. The three-volt difference is called hysteresis. There

is no need to add an external pull-up resistor when using a contact closure input.

Contact closure inputs are sampled every 10 ms and for a change of state to be

recognized, the input state must be stable for two consecutive samples. Therefore,

contact closure response is 20 ms.

Figure 10 — Binary Input Connection

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