The output signal (SIG) on the Cyclops IS, Cyclops ExP, and Sasquatch are designed as a dry contact. This means that it does not provide any voltage and the controller is expected to detect the flow of current.
How a dry contact works
A dry contact or contact switch output acts like a light switch, closing a contact when a condition is met. For this circuit to work properly, the controller must have a pull up resistor.
The Cyclops doesn’t actually have a contact switch so that it is more reliable. Instead, it has an open drain MOSFET that pulls the SIG pin is to ground (COM) through a 100 ohm impedance.
Converting to a voltage
A voltage input that can be found on many industry standard RTUs/PLCs such as:
- Emerson ROC 800
- Emerson Control Wave Micro
- ABB Total Flow
- Schneider SCADAPack
These control systems are expecting a change in voltage and do not usually have a pull up resistor built into the circuit. If you connect the Cyclops, the input will see ground when an arrival occurs, but the SIG pin will float or appear disconnected when there is no plunger arrival.
To resolve this, we must use a 10k Ohm external resistor that is pulled up to power. This ensures that the voltage input on the RTU/PLC sees a positive voltage when the Cyclops switch is open.
