Measurement-computing SWITCH AND SENSE 8/8 Manuel d'utilisateur télécharger pdf (Page 15)

Switch & Sense 8/8 User's Guide Functional Details

3-4

Relay contact protection circuit for inductive loads

If you are using the relays to control inductive loads, place a diode across the load terminals to suppress the

kickback voltage. If the diode is not present, the kickback voltage could cause the on-board processor to enter

an unstable state. To return the processor to a stable state, unplug the power cable from the Switch & Sense 8/8

and then reconnect.

A contact protection circuit is shown in Figure 3-4. For AC loads, install a metal oxide varistor (MOV).

Inductive

Load

Kickback

Diode

Relay

Figure 3-4. Relay contact protection circuit

Differential isolated digital input terminals (IP0A to IP7B)

Connect up to eight isolated digital input signals using the following screw terminal pairs:

! IP0A and IP0B ! IP4A and IP4B

! IP1A and IP1B ! IP5A and IP5B

! IP2A and IP2B ! IP6A and IP6B

! IP3A and IP3B ! IP7A and IP7B

A schematic of a single channel is shown in Figure 3-5. Each signal is applied to a bridge rectifier so that the

input is not polarity-sensitive. It can be driven by either AC (50 - 1000 Hz) or DC voltage.

The eight optically isolated (500 V) inputs can be read back as a single byte. Each input has a software-

controlled filter with a time constant of 5 ms (200 Hz). The filter is required for AC inputs, and recommended

for almost all DC inputs. Unless you have a good reason to turn off a filter, we recommend that you enable it.

1.6 K

Isolated Input

Not Polarized Circuitry Sharing

PC Ground

Filter Switc

0.1uF

47K

+5V

100K

Figure 3-5. Switch & Sense 8/8 single-channel configuration

1 2 ... 10 11 12 13 14 15 16 17 18 19

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Measurement-computing SWITCH AND SENSE 8/8 Manuel d'utilisateur Page 15