Contemporary Control Systems BASremote Installation Guide - Manual (Page 14)

TD040300-0II
14
common mechanical contacts, polarity is not an issue. The open-circuit
voltage is 24 VDC and the short-circuit current is 2 mA.
Figure 12 — 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.