Measurement Computing USB-ERB08 - Manual (Page 16)

USB-ERB08 User's Guide Functional Details
Pull-up/Pull-down switch (S2)
The Pull-up/pull-down switch (S2) sets the power-on state of each relay bank. By default, switch S2 is
configured for pull-down (relays inactive at power-up - see
). Figure 3-3
Figure 3-3. Switch S2 default configuration
PULL UP PULL DOWN
CH
CL
S2
The switch labeled CL configures relays 1 through 4, the switch labeled CH configures relays 5 through 8.
ƒ PULL UP : The relay energizes at power-up, regardless of the state of switch S1.
ƒ 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
Connect external devices to the relay contacts using the USB-ERB08 board's eight sets of screw terminals. Each
relay has a normally closed (NC), common (C), and normally open (NO) contact.
shows the screw
terminals on a typical relay channel.
Figure 3-4
Figure 3-4. Typical relay channel
NC C NO
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-ERB08, and make
sure that the signal wires do not contain live voltages.
Wire gauge
Use 12 AWG to 22 AWG wire to connect field devices. Properly insulate the wires to avoid any short circuit to
the other connections, 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") long.
Daisy chaining additional relays to the USB-ERB08
Daisy chained MCC USB Series products connect to the USB bus through the high-speed hub on the USB-
ERB08. You can daisy chain a maximum of four MCC USB Series products to a single USB 2.0 port or USB
1.1 port on your computer.
MCC USB Series products are USB 1.1 full-speed devices that provide a signaling bit rate of 12 Mb/s. The
throughput rate is shared by all devices connected to the USB bus. Use the supplied cable or an equivalent cable
when daisy chaining MCC USB Series products.
To daisy chain two or more USB-ERB08 modules, follow the steps below. This procedure assumes you already
have one USB-ERB08 connected to a computer and to an external power source. The USB-ERB08 already
connected to the computer is referred to as the connected module. The USB-ERB08 you want to daisy chain to
the connected module is referred to as the new module.
3-3