Contemporary Control Systems BASremote User Manual (firmware 3.1.x) - Manual (Page 23)

TD040300-0MF
23
Figure 9
— Contact Closure Connections
For solid-state switches, there are further concerns. It is recommended that a 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 should be connected to point B and the collector to
point A which is the more positive point. This polarity must be observed when using
solid-state devices. When an input is configured for a contact closure, the BAS Remote
sets the low-threshold to 2 V and the high-threshold to 3 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 B will quickly begin to
rise towards 24 V. Once the voltage passes the 3 V high-threshold, the input channel
will sense the “off” state. To return to the “on” state, this voltage needs to return to 2 V.
The one-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 from 20
–30 ms.