All status inputs are opto-isolated and the input impedance is greater than 22 kΩ. Input voltages ranging from –12 V to +0.8 V are considered a logic Low level, while voltages from +2.4 V to +12 V are considered a logic High level. DIP switches are used to place a 22 k pull-up resistor IN or OUT on the status input positive terminal. DIP switches are also used to set the ground terminal to internal digital D or external (E). The MEXM-1 and MEXM-2 Status input circuits are different. The MEXM-1 external ground (E) is common to all 24 Status inputs while the MEXM-2 external ground is separate for each of the 64 Status inputs. This allows complete isolation between each of the Status inputs on the MEXM-2 when the pull-up is OUT and the ground is set to the E position in Wet-contact mode.
Note: Make sure the DIP switch settings of the MEXM unit match your status input signal source (the pull-up resistors shall be IN or OUT, see images below).
Dry-contact (pull-up) configuration
When pull-up resistors are used, an open circuit is taken as a logic High and short to ground as a logic Low.
Wet-contact (external drive signal) configuration
To isolate the MEXM status inputs from other equipment, the terminal ground connection can be set to external (E) using a DIP switch. When the ground is set to external, voltage +Vin in images below must be greater than +2.4 VDC in order to activate the photodiode of the opto-coupler. In this case, an open circuit is considered as a logic Low, and a voltage higher than +2.4 VDC is considered as a logic High.
Status input DIP switches
At the factory, Status input DIP switches are set for the dry-contact configuration with the internal pull-up IN (see table below). To gain access to the status inputs DIP switches, loosen the two screws retaining the clear plastic cover to the left of the MEXM module as shown in the images below and remove the cover.
The configuration of each of the 24 (MEXM-1) or 64 (MEXM-2) status inputs can be set independently. The number written between the two DIP switch rows indicates to which input the settings are applied.
NOTE: all 64 inputs on the MEXM-2 have independant external grounds, while the 24 inputs of the MEXM-1 have a common external ground.
|Status input contact mode||Pull-up||Ground|
Status input DIP switch settings