Wavetronix Click 500 (programmable controller) (CLK-500) - Developer Guide - Manual (Page 24)

CHAPTER 1 • USING THE CLICK 500 23
Note
If you need to measure low DC voltages (e.g. 5-volt logic) you can configure the inputs
to monitor contact closures. In this state, the digital inputs can also monitor low-
level DC with the threshold set at about 2.5 VDC.
Make sure to check the polarity of the signals that you are measuring. For example, in stan-
dard NEMA cabinets the voltage signals from the traffic controller to the load switches are
not high-asserted. Instead they are low-asserted, meaning that a low-voltage indicates an
ON state and a high-voltage indicates an OFF state. These NEMA signals use 24 V logic, so
the 9 V or 11.7 V threshold is acceptable to monitor traffic controller outputs.
Note
However, be advised that these NEMA signals are only easily accessible on TS1 cabi-
nets. In newer TS2 cabinets, these signals are hidden behind a back panel. Therefore
it is suggested to use the digital inputs to measure the AC coming out of the load
switch instead of the DC inputs that control the load switch. Measuring the AC will
allow the Click 500 to act more like a conflict monitor which is designed to determine
which signal indications are on instead of which indications the controller signaled
to be on.
The 11.7 and 23.4 V thresholds are intended for applications where the supply voltage for a
device other than the Click 500 needs to be monitored. For example, these thresholds can
be used to measure 12 V and 24 V battery systems, respectively. If the batteries are lead-
acid, these thresholds represent about 25% of charge is left in the battery.
Supply Voltage Input Monitoring Circuit
The supply voltage input monitoring circuit monitors the DC voltage level used to operate
the Click 500. The 6th switch of DIP switch 2 is used to set the threshold for this circuit.
If the switch is in the ON position, the circuit will trigger an output (logical 1) when the
supply voltage drops below 22.7 VDC. If the switch is in the OFF position, the circuit will
trigger an output (logical 1) when the voltage drops below 11.6 VDC. These thresholds have
been selected for 12 or 24 VDC battery operated systems and nominally represent the case
where approximately 15% of the battery charge remains in the lead acid battery system (see
Table 1.4).