Measurement-computing USB-ERB08 Manuel d'utilisateur télécharger pdf (Page 18)

USB-ERB08 User's Guide Functional Details

Relay configuration

You can install a pull-up or pull-down resistor at the NO and NC terminals on each relay. Note that the pull-up

resistors are tied to the 5 V power and should be considered when calculating the power budget. The relay

configuration is illustrated in the following schematic.

User-installed

pull-up / pull-down resistor

GND

Screw

terminals

(3 per

relay)

GND

NO NC

Digital output

from the user

Buffer/

driver

10 k

resistor

Pull-up/pull-down

switch S2

Figure 3-6. Relay configuration

The relay contacts associated that are with each relay location are listed in . Table 3-4

Table 3-4. Relay locations and associated contacts

R1, R3, R5, R7, R10, R12, R14, R16 Relays NO contact pull-up (to USB +5 V) / pull-down

R2, R4, R6, R8, R9, R11, R13, R15 Relays NC contact pull-up (to USB +5 V) / pull-down

Relay contact protection circuit for inductive loads

When you connect an inductive load to a relay, energy stored in the inductive load can induce a large voltage

surge when you switch the relay. This voltage can severely damage the relay contacts. To limit the voltage

surge across the inductive load in a DC circuit, install a kickback diode across the inductive load. Refer to the

contact protection circuit in F . For AC loads, install a metal oxide varistor (MOV). igure 3-7

Figure 3-7. Relay contact protection circuit

Inductive

Load

Kickback

Diode

Relay

3-5

1 2 ... 13 14 15 16 17 18 19 20 21 22 23

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Measurement-computing USB-ERB08 Manuel d'utilisateur Page 18