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Chapter
2
GuardLink System Design
The design of a GuardLink circuit requires knowledge of the power requirements of the input devices and the length of the link cables. A voltage drop occurs across each tap. The cumulative voltage drop determines the number of taps that can be included in the circuit.
The GuardLink system makes it easy to monitor multiple devices over long distances when multiple access points to the hazardous area are required.
The DG safety relay monitors the GuardLink system. The GuardLink system can provide diagnostic information on each access point back to the machine control system.
The GuardLink system must be designed considering these factors:
• Voltage available at each node • Wire size
• Current flowing through each node • Power requirements for each tap
• Cable lengths • Safety device power requirements
The GuardLink system is designed to operate on a 24V DC system. The maximum continuous current on the link circuit must not exceed 4 A; the taps and link cables are rated for 4 A continuous.
Figure 6 on page 24 identifies three tap connections: T1, T2, and T3. The
voltage and safety signals are sourced to connection J1. J2 is connected to downstream taps. J3 of each tap is connected to a safety device.
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018 23
Chapter 2 GuardLink System Design
Figure 6 - Tap Connections
D1 Safety Device 1
D2 Safety Device 2
Fuse
SLO-BLO™
+ + - -
Vs=24V
Power
Supply
I1
R1
Link Cable
L1
VJ1
J1
T1
INPUT
J3
Device Cable
J2
I2
Link Cable
L2
R2
VJ2 VJ3
J1
T2
INPUT
J3
Device Cable
J2
I3
Link Cable
L3
R3
Table 3 - Key for
Item
D1, D2, D3
I
1
, I
2
, I
3
I
T1
, I
I
D1
, I
T2
D2
, I
, I
T3
1D3
L
1
R
1
, L
, R
2
2
, L
, R
3
3
T1, T2, T3
V
J1
, V
J2
, V
J3
Description
Safety devices
Current in the link cable (A)
Current required by a tap (A)
Current required by a safety device (A)
Length of link cable (m)
Resistance of wire (Ω)
Taps
Voltage at tap connector (V)
J1
INPUT
T3
J2
D3
J3
Device Cable
Safety Device 3
Terminator
System Current Calculation
The GuardLink circuit current must be calculated to determine whether a significant voltage drop occurs to a safety device.
The total system current, I
1
, is the sum of the current required by the first tap plus the current required by the device that is connected to the first tap plus the current required by the downstream circuit. The total system current must not exceed 4 A, continuous.
I
1
= I
T1
+ I
D1
+ I
2
The current in each segment of the GuardLink circuit is calculated in a similar fashion.
I
2
= I
T2
+I
D2
+ I
3
I
3
= I
T3
+ I
D3
The total system current, I
1 sum of the tap currents.
, is therefore the sum of the device currents plus the
I
1
= Σ I
T
+ Σ I
D
24 Rockwell Automation Publication 440R-UM015C-EN-P - April 2018
GuardLink System Design Chapter 2
Voltage Drop Consideration
With the potential of using up to 32 taps and long cable lengths between taps, the voltage available to the safety devices at connector J3 must be calculated.
The voltage available to the safety device has two components:
• The voltage drop due to the wire resistance of the cables
• The voltage drop within the tap
The resistance of the recommended 18 AWG cordsets and patchcords is
(0.0218 ohms/m (0.00664 ohms/ft). The wire resistance of the cordset from the power supply to tap 1 (R
1
) is:
R
1
= 0.0218 * L
1
The wire resistance must be considered for both the power and ground; therefore the voltage drop is multiplied by two. The voltage at connector J1 of tap T1 (V
J1
) is:
V
J1
= 2 * I
1
* R
1
The tap has a small voltage from connector J1 to J2. The typical voltage at connector J2 (V
J2
) drop through the tap from J1 to J2 is:
V
J2
= V
J1
- (2 * 0.028V)
The voltage available at connector J3 is dependent on the device that is connected to J3. The typical voltage drop from J1 to J3 is 0.4V when the device uses 50 mA.
V
J3
= V
J1
- 0.4V (typical)
IMPORTANT The voltage drop from J1 to J3 can be as high as 1.2V with a maximum load of 500 mA at the highest rated ambient temperature.
The taps consume 25 mA when OFF. The EMSS taps consume an additional
15 mA (7.5 mA per channel) when the contacts are closed. The OSSD taps consume an additional 6 mA (3 mA per channel), when the outputs are ON.
A spreadsheet can be used to calculate the voltage available to the safety device.
Table 4 on page 26 shows the voltage available to the safety device of a number
of different devices. Assuming that the power supply voltage is set to 24V, and the cable is the recommended 18 AWG, the voltage available to the safety devices is shown in the right-hand column.
When guard locking devices are used in the circuit, the taps and wiring components are subjected to momentary surges in current. With the sequential operation of the lock/unlock command, the momentary surges should not adversely affect the performance of the GuardLink circuit.
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018 25
Chapter 2 GuardLink System Design
The operating voltage specification of the tap is 20.4…26.4V. In the example that is shown in
, the voltage at J1 of tap 6 has fallen below the lowest supply voltage specification of 20.4V DC. This system is not feasible, and remedial action must be taken (see
).
IMPORTANT
assumes the following:
• Supply voltage = 24V
• Link cable wire gauge = 18 AWG
• Link wire resistance = 0.0218 ohms/m
Table 4 - Voltage Calculation at 24V Supply
14
15
12
13
10
11
8
9
6
7
4
5
2
3
Tap
1
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
0 (0)
0 (0)
Cable Length
[m (ft)]
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
Safety Device
SensaGuard Ser A
SensaGuard Ser A
Lite Lock 440G-LZ
800F E-stop
LifeLine 4
LifeLine 5
TLSZR-GD2 PLe
TLSZR-GD2 PLe
Lite Lock 440G-LZ
SensaGuard Ser A
SensaGuard Ser A
Mechanical Switch
Mechanical Switch
—
—
40
0
81
40
0
135
135
135
81
Tap + Device
Current (mA)
81
81
135
40
40
81
161
80
40
0
0
647
512
377
242
Total Current
(mA)
1105
1024
943
808
768
728
18.81
18.75
18.73
—
—
19.73
19.36
19.10
18.92
J1 Voltage
(V)
23.22
22.49
21.82
21.25
20.70
20.19
18.41
18.35
18.33
—
—
19.33
18.96
18.70
18.52
J3 Voltage
Typical (V)
22.82
22.09
21.42
20.85
20.30
19.79
26 Rockwell Automation Publication 440R-UM015C-EN-P - April 2018
GuardLink System Design Chapter 2
To remedy the example in Table 4 , the supply voltage can be increased from
24V to 26V as shown in Table 5 . Now, all 13 taps meet the minimum voltage
specification of 20.4V at connector J1.
IMPORTANT
assumes the following:
• Supply voltage = 26V
• Link cable wire gauge = 18 AWG
• Link wire resistance = 0.0218 ohms/m
14
15
12
13
10
11
8
9
6
7
4
5
2
3
Tap
1
Table 5 - Voltage Calculation at 26V Supply
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
0 (0)
0 (0)
Cable
Length
[m (ft)]
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
15 (49.2)
Safety Device
SensaGuard Ser A
SensaGuard Ser A
Lite Lock 440G-LZ
800F E-stop
LifeLine 4
LifeLine 5
TLSZR-GD2 PLe
TLSZR-GD2 PLe
Lite Lock 440G-LZ
SensaGuard Ser A
SensaGuard Ser A
Mechanical Switch
Mechanical Switch
—
—
40
0
81
40
0
135
135
135
81
Tap + Device
Current (mA)
81
81
40
81
135
40
161
80
40
0
0
647
512
377
242
Total Current
(mA)
1105
1024
943
808
768
728
20.81
20.75
20.73
—
—
21.73
21.36
21.10
20.92
J1
Voltage
(V)
25.22
24.49
23.82
23.25
22.70
22.19
20.41
20.35
20.33
—
—
21.33
20.96
20.70
20.52
J3 Voltage
Typical (V)
25.82
24.09
23.42
22.85
22.30
21.79
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018 27
Chapter 2 GuardLink System Design
Tap Cabling
The GuardLink system was designed with the intent of minimizing wiring by using quick-disconnect patchcords, while also allowing some manual wiring to terminals, when pinout incompatibilities exist.
Figure 7 shows the recommended cable options for the various stages of a
GuardLink system (to show the cable options only two taps are required, a full system has 32 taps). These cables are red-colored, PVC, unshielded, with epoxy-coated hardware. Although any color jacket can be used, the red color is preferred to indicate a safety circuit.
Visit ab.rockwellautomation.com/Connection-Devices/DC-Micro-Cordsetsand-Patchcords for other options, like right-angle connectors, stainless steel couplings, and shielded cables.
To maintain the safety integrity of the GuardLink signal, the wiring distance between taps is limited to 30 m (98.4 ft) and requires 18 AWG (0.82 mm2) wire. If the distance between devices is greater than 30 m (98.4 ft), then a tap must be inserted at least every 30 m (98.4 ft). A field-attachable quickdisconnect can be wired as a shorting plug for the device connection. The wiring distance between taps and the safety device is limited to 10 m (32.8 ft), and requires at least 24 AWG (0.2 mm2) wire size.
Figure 7 - Recommended Cable Options (1)
Safety Device
889D-F5NCDMx
5-wire Patchcord or
889D-F8NBDMx
8-wire Patchcord
10 m (32.8 ft) length, max
INPUT
889D-M5NCx
5-wire Cordset or
889D-M8NBx
8-wire Cordset
10 m (32.8 ft) length, max
Safety Device
INPUT
White
DG
Safety
Relay
Black Brown Blue
+ + - -
24V
Power
Supply
889D-F4NEx
4-wire Cordset
30 m (98.4 ft) length, max
889D-F4NEDMx
4-wire Patchcord
30 m (98.4 ft) length, max
889D-418-DM2
Terminator
28
(1) Replace the x with 0M3 (0.3 m [0.984 ft]), 0M6 (0.6 m [1.968 ft]), 1 (1 m [3.28 ft]), 2 (2 m [6.56 ft]), 5 (5 m [16.4 ft]), 10 (10 m
[32.8 ft]), 15 (15 m [9.2 ft]), 20 (20 m [65.6 ft]), or 30 (30 m [98.4 ft]) for standard cable lengths.
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018
Terminator
GuardLink System Design Chapter 2
The terminator (
Figure 8 ), must be installed on the last tap to complete the
link connection. The terminator contains internal electrical components specifically for a GuardLink system; other terminators cannot be used as substitutes.
Figure 8 - Terminator — Catalog Number 898D-418U-DM2
Tap Replacement
Response Time
A GuardLink tap can be replaced with the same type of tap while the link is powered. When the connections are remade; the GuardLink circuit recovers automatically.
The GuardLink circuit has a fast response time. When a safety device opens, the tap responds within 5 ms. The GuardLink safety signal then travels upstream to the DG safety relay, which takes an additional 35 µs through each upstream tap.
Figure 9 shows an example GuardLink safety circuit with six taps. In this
example, a SensaGuard rectangular flat pack interlock, which is connected to
Tap 4, opens.
Figure 9 - Response Time Example Calculation
SensaGuard
Opens
Tap 1 Tap 2 Tap 3
Upstream
Tap 4 Tap 5
Downstream
Tap 6
DG Safety Relay
Single Wire Safety Out
100S-C09EJ
Safety
Contactors
Rockwell Automation Publication 440R-UM015C-EN-P - April 2018 29
Chapter 2 GuardLink System Design
The safety system response time for the system that is shown in Figure 9
is
listed in Table 6 . The time from when the SensaGuard interlock opens to the
time when the 100S contactors drop out is 169.105 ms. The time from when the SensaGuard interlock opens to the time when the SWS signal turns OFF is
114.105 ms.
Table 6 - Example Response Time Calculation
Component
SensaGuard
(1)
Tap 4
Tap 3
Tap 2
Tap 1
DG Safety Relay
100S Contactor
(2)
Total
(1) See publication 440N-IN008 .
(2) See publication 100-TD013 .
DG Output
13/14, 23/24
54.0
5.0
0.035
0.035
0.035
60.0
50.0
169.105
Response Time [ms]
DG Output
SWS (X2)
54.0
5.0
0.035
0.035
0.035
55.0
0.0
114.105
IMPORTANT
and Table 6 show only a portion of a complete safety system.
Additional time (for example, for motor stopping time and the response time of additional components that are connected to the SWS signal) must be considered.
30 Rockwell Automation Publication 440R-UM015C-EN-P - April 2018

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