Pilz PZE 9 safety relay

Pilz PZE 9 Safety Relay Contact Expansion Module: A Complete Guide to Selection, Wiring, and Field Troubleshooting

In the safety control circuit of industrial machinery, it is often necessary to extend safety signals such as emergency stop and protective door switch to multiple actuators or contactors. Although basic safety relays (such as PNOZ X series) or programmable safety systems (such as PNOZmulti) already provide a certain number of safety contacts, the contact capacity or quantity of the original equipment may be insufficient when multiple loads (such as multiple motor contactors, valves, or lights) need to be cut off simultaneously. At this point, a contact extension module is needed that can replicate and add secure output contacts without compromising the original security level.

Pilz's PZE 9 is precisely such a classic contact extension module. It is not an independent safety assessment device, but rather serves as a subordinate extension of the base unit, monitoring the status of its internal relays through the feedback loop of the base unit. This article is based on the PZE 9 operation manual (version 1001635-EN-10), and systematically introduces various power versions, installation and wiring points, coordination methods with different basic units, safety characteristic data, as well as diagnosis and troubleshooting methods for common faults on site (such as contact welding, input circuit disconnection, or grounding faults) of this module. Whether you are renovating an old electrical cabinet or planning a safety circuit in a new project, this article will provide valuable practical references.

Product Overview and Model Selection of PZE 9

2.1 Product positioning and basic functions

PZE 9 belongs to the contact extension module without power outage delay (Add on device without delay on de excitation). Its main function is to:

Receive output signals from basic units such as emergency stop relays and programmable safety systems.

Copy the state of the input circuit to 8 momentary safety normally open contacts (N/O) and 1 auxiliary normally closed contact (N/C).

Monitor the internal relay contacts through feedback loops to ensure the transmission of safety functions.

Key features:

Positive guided relay outputs comply with EN 60947-5-1.

Input circuit support: single channel, dual channel (without cross short circuit detection), or dual channel with cross short circuit detection.

LED status indicators: Power, CH.1 (channel 1 contact closed), CH.2 (channel 2 contact closed).

Wide working voltage range: DC 24V, AC 24V/42V/48V/110-120V/230-240V.

2.2 Model Overview and Selection Suggestions

Order number, power supply voltage type, typical application scenarios

774150 24 V DC with PNOZmulti or PLC safety output coordination

774140 24 V AC traditional AC control cabinet, directly taken from the control transformer

774141 42 V AC AC for specific ships or humid environments (safe extra low voltage)

774142 48 V AC AC control circuit for some old-fashioned machine tools

774143 110-120 V AC North American or specific industry standard voltage

774148 230-240 V AC Common Frequency Voltage in Europe and Asia

Selection guide: Prioritize the 24V DC version (774150), as modern safety systems and PLCs generally output 24V DC, and DC power supply is more stable and responsive. If there is already an AC control power supply on site that cannot be modified, select the corresponding AC version. Note that the maximum allowable total cable resistance in the input circuit for the AC version is different from that for the DC version (see technical parameters for details).

Installation and wiring specifications

3.1 Mechanical Installation

Environmental requirements: The protection level of the control cabinet should be at least IP54. The module itself has a shell protection of IP40 and a wiring terminal protection of IP20.

Installation method: 35mm DIN rail (EN 60715). Use the card slot on the back of the module to insert the guide rail. When installing vertically, fixed clips (such as stoppers or end corners) should be added at the upper and lower ends to prevent vibration slippage.

Heat dissipation and spacing: No special heat dissipation is required, but it should be avoided to closely adhere to high-power heating devices (such as frequency converters and large resistors). The ambient temperature range is -10 ℃ to+55 ℃.

3.2 Core points of electrical wiring

3.2.1 Power Supply

DC version (24V DC): The power supply must comply with SELV/PELV (Safety Extra Low Voltage) standards and have protective electrical isolation. A1 is connected to L+(positive), A2 is connected to L - (negative). Residual ripple is allowed at 160% (i.e. up to a peak of 38.4V).

Communication version (24/42/48/110-120/230-240V AC): A1 is connected to the phase line (L1), A2 is connected to the neutral line (N). The frequency is 50/60Hz and the power consumption is 7VA.

3.2.2 Input circuit (Y1-Y2 terminals)

PZE 9 receives safety output signals from the base unit through terminals Y1 and Y2. According to the type of basic unit and the presence or absence of short-circuit detection, there are three types of wiring methods:

Configuration wiring method Maximum total cable resistance (Rmax) Applicable basic unit example

Single channel Y1 is connected to a safety contact of the basic unit, Y2 is directly connected to A2 (power supply negative/neutral) 24V DC: 50 Ω; 24V AC: 80 Ω PNOZ X (single channel output)

Dual channel (without short circuit detection) Y1 and Y2 are respectively connected to the two safety contacts of the basic unit, with no cross short circuit detection between them. 24V DC: 100 Ω; 24V AC: 160 Ω PNOZ X (dual channel)

Dual channel (with short circuit detection) Y1 and Y2 are connected to two safety semiconductor outputs of the base unit, which need to have cross short circuit monitoring DC: 5 Ω; AC: 10 Ω PNOZmulti or safety PLC

Important: Calculation basis for cable length

Lmax=Rmax/(Rl/km)

L max=R max/(R l/km)。 For example, using a 1.5mm ² copper cable (with a resistance of approximately 12.1 Ω/km), the maximum length under 24V AC dual channel short-circuit detection is approximately 160/12.1 ≈ 13.2 kilometers (which may be much smaller in actual engineering due to the influence of distributed capacitance). The manual provides resistance limits, but in practice, voltage drop should also be considered.

3.2.3 Feedback loop (Y3-Y4 terminals)

Feedback loop is the key to ensuring the integrity of safety functions. The basic unit determines whether the internal output relay of PZE 9 is working properly by monitoring the circuit between Y3-Y4. Standard connection method:

Connect the Y3 terminal of PZE 9 to the feedback input terminal of the base unit (such as Y1 or Y2 of PNOZ X), and connect Y4 to another feedback input of the base unit or the positive pole of the 24V DC power supply (depending on the base unit model). The schematic diagram in the manual indicates that Y1 and Y2 serve as feedback inputs for the base unit (such as PNOZ X) and are connected in series with the feedback loop of PZE. More specifically, the auxiliary contacts 91-92 of PZE 9 are used to display status, but the feedback loop itself is already connected internally? Reading manual: Y3 and Y4 are directly introduced, and users need to connect them to the feedback loop of the basic unit. In fact, PZE 9 has auxiliary contacts 91-92 inside, but the feedback loop wiring diagram shows that Y3/Y4 are connected in series in the feedback loop of the base unit. The operator should strictly follow the manual of the selected basic unit for wiring.

Attention: Auxiliary contacts 91-92 (N/C) are used for indication purposes (such as connecting indicator lights or PLC inputs) and must not be used for safety circuits. The feedback loop must use Y3-Y4 dedicated terminals.

3.2.4 Output Contact Wiring

Safety contacts: 8 pairs of normally open, terminal numbers 13-14, 23-24, 33-34, 43-44, 53-54, 63-64, 73-74, 83-84. These contacts can be used to cut off hazardous sources (such as motor contactors, valves).

Auxiliary contacts: 91-92 (normally closed), cannot be used for safety functions.

Fuse protection: To prevent contact welding, a suitable fuse or circuit breaker must be connected in series before the output contact. Recommended manual:

Safety contacts: fast fuse 10A, slow speed 6A, gG type 10A, circuit breaker (B/C characteristics) 6A.

Auxiliary contacts: fast fuse 4A, slow speed 2A, gG type 4A, circuit breaker 2A.

Wiring material: Copper wire is used, with a temperature resistance rating of 60/75 ° C. The torque of the screw terminal is 0.5Nm, and the stripping length is 6mm. The maximum size of single core flexible wire is 4mm ² (AWG 10), and the maximum size of double core flexible wire with the same cross-section is 2.5mm ² (AWG 14).

3.3 EMC and Wiring Rules

Control cables (input, feedback loops) should be routed separately from power cables (motors, frequency converters), with a minimum spacing of 200mm, or shielded cables should be used.

For capacitive and inductive loads, suppression circuits (such as RC absorbers, varistors, or freewheeling diodes) must be installed at both ends of the contacts to extend contact life and reduce interference.

Important warning: Do not switch small currents (such as a few milliamps) on contacts that have previously passed large currents, otherwise poor contact may occur due to surface oxidation of the contacts. If it is necessary to switch low-level signals, a gold-plated contact dedicated relay should be used.

Functional principle and safety working logic

4.1 Normal working sequence

Power on: POWER LED lights up.

Input circuit closure (basic unit safety contact closure):

Internal relay excitation, 8 safety contacts (13-84) closed, auxiliary contacts 91-92 disconnected.

CH.1 and CH.2 LEDs light up simultaneously (indicating that both channels are closed).

Input circuit disconnected (press emergency stop or open protective door):

The internal redundant contacts are immediately disconnected, the safety contacts are opened, and the auxiliary contacts are closed.

CH.1 and CH.2 LEDs turn off.

4.2 Safety features and fault detection

PZE 9 itself does not perform logical judgment, it relies on the feedback loop of the basic unit to detect its own faults:

Contact fusion welding detection: If a group of safety contacts cannot be opened due to overcurrent fusion welding after the input circuit is disconnected, the feedback circuit will remain conductive (because Y3-Y4 is still internally connected), and the basic unit will detect this abnormality during the next reset, preventing restart.

Input circuit ground fault: If Y1 or Y2 is short circuited to ground, the internal monitoring circuit of PZE 9 will cause the output relay to lose power and the safety contacts to open (the manual clearly states: "Earth fault in the input circuit: The output relays de energy and the safety contacts open.").

Feedback loop grounding fault: Detection depends on the capability of the base unit.

These designs enable PZE 9 to safely expand contacts without compromising the original safety circuit level.

Safety feature data and lifespan chart

5.1 Safety level parameters

The security level that PZE 9 can achieve depends on the connected base unit. But the data of the module itself is as follows (from the safety feature data diagram in the manual, please refer to the original figure values). According to a typical Pilz contact extension module, the B10d value (median number of dangerous failure cycles) of PZE 9 is usually high, and the PFH (probability of dangerous failure per hour) is generally at the 1.0E-8 level. The safety related characteristic values stated under safety related characteristic data can only be achieved if the base unit also exhibits these safety characteristic values

Suggest using PAScal software to calculate the overall security function results. Common applications:

Combined with PNOZ X, it can achieve SIL CL 3, PL e (highest level).

Combined with PNOZmulti, it can also achieve SIL CL 3 and PL e.

5.2 Contact Life Curve (Service Life Chart)

The manual provides a Service Life graph, with the x-axis representing the number of switching cycles and the y-axis representing the contact current (A). The curves correspond to different load types (AC15/DC13). For example, under AC15 (230V) load, the contact life is about 4 million times when the current is 0.2A. In practical applications, if the expected total number of switches is lower than this value, the PFH value given in the manual can be used for calculation; If it exceeds, mechanical wear and tear should be considered.

Measures to extend the lifespan of contacts:

Install suppression circuits (RC, varistor, freewheeling diode) on inductive loads.

Avoid overcurrent (exceeding the rated value).

For DC inductive loads, freewheeling diodes can increase the contact life by several times.

Common on-site troubleshooting

6.1 Fault phenomenon: PZE 9 is powered on but the safety contacts do not engage after the input is closed

Possible reasons:

The input circuit is not truly conducting (there is no voltage difference between Y1-Y2).

The basic unit has not output a safety signal.

Feedback loop wiring error or open circuit.

Internal relay malfunction.

Troubleshooting steps:

Measure the voltage between Y1 and Y2: In the closed state, it should be 24V DC (or AC power supply voltage, for AC models). If it is 0V, check if the safety output of the basic unit is normal.

Check feedback loop Y3-Y4: Measure at the feedback input of the base unit to ensure that the loop is connected. When using a multimeter to measure Y3-Y4 of PZE 9 in the resistance range (after power failure), it should be a short circuit (when the relay is not excited? In fact, Y3-Y4 may be an open circuit when it is not excited? Please refer to the internal circuit diagram. The manual does not provide a detailed internal circuit, but the feedback loop is usually composed of auxiliary contacts and safety contacts. Insurance practice: Check if the feedback loop indicator light on the basic unit is on.

If all the above are normal, replace the PZE 9 module.

6.2 Fault phenomenon: After the input circuit is disconnected, the safety contact cannot be opened (critical situation)

Phenomenon: After resetting the emergency stop button, the device can still start (i.e. the touch point is stuck).

Reason: Welding of safety contacts due to overcurrent or frequent switching.

handle:

Immediately cut off the main power supply.

Measure the resistance of each safety contact with a multimeter (in power-off state), which should normally be infinite. If the resistance of a pair of contacts is close to 0 Ω, it indicates that they have been welded.

Replace the entire PZE 9 module (contact repairs are not allowed).

Check if the load current and suppression circuit are correct. If necessary, install a lower speed fuse or increase the contact rating.

6.3 Fault phenomenon: The basic unit cannot be reset (startup prohibited)

Reason: The feedback loop of the basic unit detected that the internal contacts of PZE 9 did not open properly (possibly due to previous welding or mechanical jamming causing the feedback loop to remain conductive after the input loop was disconnected).

troubleshoot

Close the input circuit of PZE 9 (leaving Y1-Y2 open) and observe whether the CH.1 and CH.2 LEDs are turned off. If the LED is still on, it may be an input circuit ground fault or an internal module fault.

Measure the resistance of Y3-Y4: normally it should be an open circuit (because the relay is not excited). If there is a short circuit, it indicates that the safety contact or internal feedback contact is stuck.

Replace PZE 9 and check the external wiring.

6.4 Fault phenomenon: The status of CH.1 and CH.2 indicator lights is inconsistent (one on and one off)

Reason: Inconsistent dual channel input signals (such as asynchronous two safety outputs of the base unit), or one of the channels is disconnected.

handle:

Check if both channels of the output of the basic unit are closed properly.

Measure the voltage of Y1 and Y2 at the common terminal (A2) simultaneously.

Check the cable connections and terminal fastening.

6.5 Fault phenomenon: POWER LED flashes or does not light up

Reason:

The power supply voltage exceeds the tolerance (-15%/+10%). The 24V DC version allows 20.4V~26.4V; If it is below 20.4V, the module may not work reliably.

The power ripple is too large or there is a momentary drop.

Solution: Use a stable regulated power supply and check if the transformer capacity is sufficient for the AC version.

Regular Inspection and Maintenance Plan

According to EN ISO 13849 and the Machinery Directive, the effectiveness of safety functions must be regularly checked.

Frequency of required safety level inspection

SIL CL 3/PL e at least once a month

SIL CL 2/PL d at least once a year

Inspection steps:

Disconnect the input signal of the basic unit (such as opening the emergency stop button or protective door).

Confirm that the CH.1 and CH.2 LEDs of PZE 9 are turned off, and all safety contacts are disconnected (load stopped).

Restart the basic unit (reset), confirm that the safety contacts of PZE 9 are closed, and the CH LED lights up.

If the basic unit cannot be reset, it indicates that the feedback loop has detected an abnormality (possibly due to contact welding), and the above-mentioned troubleshooting should be carried out.

Annual in-depth maintenance:

Check if all terminal screws are loose (torque 0.5Nm).

Check if the fuse is intact and its specifications comply with the manual requirements.

Clean the cabinet dust and maintain heat dissipation.

Connection instance with basic unit

8.1 Cooperate with PNOZ X safety relay (dual channel no short circuit detection)

PNOZ X output terminals 13-14 are connected to Y1 and Y2 (dual channels) of PZE 9.

The feedback loop input terminals (Y1 and Y2, with different terminal numbers for different models) of PNOZ X are connected in series with Y3 and Y4 of PZE 9.

Connect A2 of PZE 9 to 0V and A1 to 24V DC.

8.2 Cooperate with PNOZmulti or safety PLC (with short circuit detection)

The two semiconductor outputs of the safety PLC (requiring cross short circuit monitoring) are directly connected to Y1 and Y2.

Due to the low resistance (<5 Ω) of semiconductor output, it meets the wiring requirements of "dual channel with short circuit detection" (Rmax=5 Ω for DC).

The feedback loop is connected according to the safety PLC manual.

8.3 Expanding Multiple PZE 9 Modules

If more than 8 safety contacts are required, can the output of one PZE 9 be used as the input of the next PZE 9? not allow. Because the input loop of PZE 9 requires a safe output from the base unit, and cannot come from the output of another expansion module (which would bypass feedback monitoring). The correct approach is for the base unit to simultaneously drive multiple PZEs 9 (parallel input), with each PZE9's feedback loop separately connected to the base unit's feedback loop (in series).

Common errors and avoidance

Auxiliary contacts are used for safety circuits: 91-92 must not be used for safety disconnection, only for indication.

Not using feedback loop: If Y1-Y2 is directly powered without connecting Y3-Y4 to the base unit, internal faults of PZE 9 cannot be detected, and the safety level will be reduced.

Excessive specification of fuse: Using a fuse larger than the recommended value may result in the inability to disconnect the contacts during welding, leading to safety failure.

The input circuit of the AC version uses a DC power supply: The AC version is designed for sine waves, and the DC power supply may not be able to detect the zero crossing point properly, resulting in the relay not closing or shaking.

Neglecting contact life: In high current applications with frequent switching, it is necessary to calculate the expected number of switches and compare them with the life chart. If necessary, larger capacity expansion modules (such as PZE 24V DC 16A version) should be selected.