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System installation, Category 4, Mmd-ta-11b / mmd-ta-12b muting module – Banner MMD-TA-11B Muting Modules User Manual

Page 25

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P/N 116390 rev. C

23

Banner Engineering Corp.

Minneapolis, U.S.A.

www.bannerengineering.com • Tel: 763.544.3164

MMD-TA-11B / MMD-TA-12B Muting Module

Instruction Manual

System Installation

Category 4

To ensure a category 4 application, any device connected to the

SSI and MSSI inputs must meet certain criteria. For example, a

“type 4” safety light screen (curtain) that meets IEC 61496-1/-2 is

a device that meets category 4 requirements.
In a category 4 application, a single fault must not cause the loss

of the safety function. The fault must be detected at or before

the next demand of the safety function, and an accumulation of

faults also must not cause the loss of the safety function.
This is usually accomplished by the use of redundant safety

inputs or outputs from the safety-rated device that are monitored

to detect certain faults. These faults include:
• Increased response time
• Prevention of one or more safety outputs (OSSDs) going to the

OFF-state

• A short circuit between channels
NOTE: Solid-state safety outputs, such as those from

EZ-SCREEN Type 4 safety light screens, typically

achieve this level of fault tolerance by self-monitoring a

pulsing of the outputs. Safety devices with hard-contact

or relay outputs must be connected in a “4-wire” method

as shown in Figure 3-15c.

The principle of fault exclusion must be incorporated into the

design and installation to either eliminate, or reduce to an

acceptable (minimal) level of risk, the possibility of catastrophic

failures/faults that could result in the loss of the safety function.

Figure 3-15a. MSSI and SSI Category 4 interfacing: two

positive-opening switches per single guard

(a)

MSSI or SSI

(b)

(c)

(d)

A1

X6

X5

X7

X8

S12

S11

S21

S22

+24V dc

0V

MMD-TA-..B

A2

Figure 3-15b. MSSI and SSI Category 4 interfacing: category 4

safeguarding device with output fault monitoring

(e.g., EZ-SCREEN or AOPD Type 4 per IEC 61496-

1/-2)

+24V dc

EZ-SCREEN

Type 4

0V

(a)

MSSI or SSI

(b)

(c)

(d)

MMD-TA-..B

A1

S12

S11

A2

+

+

S22

S21

X6

X5

X8

X7

Figure 3-15c. MSSI and SSI Category 4 interfacing: category 4

safeguarding device with relay outputs (e.g.,

MINI-SCREEN or AOPD Type 4 per IEC 61496-1/-2)

(a)

MSSI or SSI

(b)

(c)

(d)

A1

X6

X5

X7

X8

S12

S11

S21

AOPD

Type 4

S22

+24V dc

0V

MMD-TA-..B

A2

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