USB-ERB24 User's Guide
Functional Details
11
The switch labeled
A
configures relays 1 through 8, the switch labeled
B
configures relays 9 through 16, the
switch labeled
CH
configures relays 17 through 20, the switch labeled
CL
configures relays 21 through 24.
NON-INVERT
: When
0
is written or read back through the USB bus, the relays are not energized.
INVERT
: When
0
is written or read back through the USB bus, the relays are energized.
Switch settings do not affect the power-on condition. Use InstaCal to read the current logic setting for each
module group.
Pull-up/down switch (S2)
The pull-up/down switch (S2) sets the power-on state of each relay bank. By default, switch S2 is configured
for pull-down (relays are inactive at power-up – see Figure 7).
Figure 7. Switch S2 default configuration
The switch labeled
A
configures relays 1 through 8, the switch labeled
B
configures relays 9 through 16, the
switch labeled
CH
configures relays 17 through 20, the switch labeled
CL
configures relays 21 through 24.
PULL UP
: The relay energizes at power-up, regardless of the state of switch S1.
PULL DOWN
: The relays are not energized at power-up.
Use InstaCal to read the current power-on state setting for each module group.
Screw terminals and relays
Connect external devices to the relay contacts using the USB-ERB24 set of 24 screw terminals. Each relay has a
normally closed (NC), common (C), and normally open (NO) contact. Figure 8 shows the screw terminals on a
typical relay channel.
Figure 8. Typical relay channel
Each screw terminal is identified with a label on the board and on the underside of the enclosure lid.
Caution!
Before connecting wires to the screw terminals, turn off the power to the USB-ERB24, and
make sure that the signal wires do not contain live voltages.
Use 12-22 AWG wire for your signal connections. Properly insulate the wires to avoid any
short circuit to the other channels, ground, or other points on the board.
Caution!
Keep the length of stripped wire at a minimum to avoid a short to the enclosure. When
connecting your field wiring to the screw terminals, use the strip gage on the terminal strip, or
strip to 5.5 - 7.0 mm (0.215 to 0.275 in.) long.