Pilz PSWZ X1P static monitoring

Pilz PSWZ X1P Safety Static Monitoring Relay: A Complete Guide from Wiring Configuration to Troubleshooting

Introduction: Why is safe static monitoring necessary

In industrial machinery and equipment, the accidental start or incomplete stop of dangerous moving parts is often the main cause of safety accidents. Especially for large motors, fans, stamping equipment, etc. with inertial sliding, simply cutting off the main power supply cannot immediately eliminate the danger - the motor rotor may continue to rotate for seconds or even tens of seconds. At this point, if maintenance personnel enter the protected area too early, they may encounter serious mechanical injuries.

PSWZ X1P is a specialized safety static monitoring relay launched by PILZ company. It measures the regenerative voltage generated during the motor deceleration process through independent redundant channels, and only allows safe outputs (such as contactors) to be reconnected when the voltage is below the set threshold (static threshold). This device complies with PL e/Category 4 of EN ISO 13849-1 and SIL CL 3 level of EN IEC 62061, and is suitable for applications that require the highest safety integrity. This article will provide a detailed operation guide for on-site engineers from six aspects: installation, wiring, parameter setting, application examples, fault diagnosis, and maintenance testing.

Product Overview and Key Features

The PSWZ X1P has two main sub models, differing in response threshold range and connection terminal type (spring terminal or screw terminal). The core functions are as follows:

Redundant measurement: Two independent channels monitor the voltage between different phases of the motor winding (L1-L3 and L2-L3), with "simultaneous monitoring" between channels (maximum 7 seconds); If the time for the voltage of two channels to fall below the threshold is not consistent and exceeds the set value, a fault latch will be triggered.

Self check function: After each power on or reset, the device simulates exceeding the release value and detects an open circuit in the measurement circuit. It automatically tests the output relay and feedback loop for approximately 1.5 seconds.

Output configuration:

2 safety normally open contacts (momentary, 13-14, 23-24) - used to cut off hazardous power circuits.

1 auxiliary normally closed contact (41-42) - used for status indication, not for safety circuits.

Two semiconductor outputs: Y32 (switch status signal, high level valid) and Y35 (fault signal).

Wide voltage power supply: AC/DC 24-240V, suitable for most industrial sites worldwide.

Optional input range:

Standard type: Response threshold 20-500 mV, release value=2 x response value.

High sensitivity type: 7.5-500 mV (order ending in 777951).

High threshold type: 120-3000 mV (order ending in 777950).

Feedback loop monitoring: The Y1-Y2 terminals are used to monitor the feedback contacts of the external contactor, ensuring that the external contactor is indeed in the disconnected state before executing the safety output.

Selection key: The appropriate input range must be selected based on the residual magnetic voltage of the motor (i.e. the residual induced voltage generated by the motor winding after shutdown). The response range should cover the residual magnetic voltage, otherwise it is impossible to correctly detect stillness.

Installation and wiring

1. Mechanical installation

Installed in a control cabinet with a minimum protection level of IP54.

Install using a 35mm DIN rail and use the groove on the back of the device to insert the rail. When installing vertically, it is recommended to use fasteners (such as stoppers or end corners) to prevent slipping.

Dimensions: Width 45mm x Height 94mm x Depth 121mm (Spring Terminal Type Height 101mm).

2. Power wiring

Terminals A1 and A2: Connect 24-240V AC/DC (wide range automatic adaptation). Attention: Can there be no polarity distinction in DC? AC/DC is acceptable, but for DC, it is recommended to connect the positive pole to A1.

Power supply capacity: AC 5VA/DC 3W.

Allowable power interruption time: ≥ 20ms will cause output disconnection (safety side).

3. Input circuit (motor measurement wiring)

Select wiring method based on motor type:

Instructions for wiring methods of motor types

Three phase motor (standard) L1 → motor U phase, L2 → motor V phase, L3 → motor W phase. Two channels for measuring line voltages L1-L3 and L2-L3 are redundant with each other

Single phase AC motor L1 → motor live wire (L), L2 → motor neutral wire (N), L3 → motor neutral wire (N). In a single-phase system, the two channels are actually the same measurement point, but they still need to be electrically separated

DC motor L1 → motor positive pole, L3 → motor negative pole, L2 suspended or connected in parallel can only achieve single channel measurement, at which point the safety performance is reduced? Note that the manual does not recommend direct current, but it can be used in single-phase mode. To achieve the highest level of safety, three-phase motors are optimal

Maximum measured voltage: 690V AC/DC (600V when UL certified), frequency range 0-3kHz, suitable for variable frequency drive motors.

Input resistance: 1.3M Ω, which will not significantly affect the motor circuit.

Cable length limit: maximum total circuit resistance of 1.3M Ω, actual cable length=1.3M Ω/(cable resistance per kilometer). For example, if the resistance of a 1.5mm ² copper wire is about 13.7 Ω/km, the maximum length is about 95km (theoretical value, actual consideration of distributed capacitance and interference, it is recommended to control within 1000m).

Shielding requirement: When using a frequency converter, a shielded cable must be used to connect the PSWZ X1P to the motor, and the shielding layer must be grounded on the motor side.

4. Feedback loop (Y1-Y2)

It is necessary to connect the normally closed auxiliary contacts of the external contactor to form a feedback loop.

When the safety contact is disconnected, the external contactor should be disconnected accordingly, and its normally closed auxiliary contact should be closed, thereby closing the feedback loop. The PSWZ X1P will only allow the safety output to be re closed when the feedback loop is closed and both measurement channel voltages are below the response value.

If there is no external contactor (only used to directly cut off low-power loads), Y1-Y2 can be short circuited. But at this time, the monitoring function of the external contactor will be lost, and it is not recommended to use it for high safety levels.

5. Semiconductor output

Y32 (switch status output): High level (≈ 24V) indicates that the safety contact is closed.

Y35 (Fault Output): High level indicates a fault (such as synchronous timeout).

Both outputs require external 24V power supply (load capacity 50mA, short circuit protection). Cannot directly drive high-power loads.

6. Reset input (RESET)

The falling edge of the low level (<5V) after applying a high level (>15V) between terminal Y30 and the common terminal (0V) can reset the fault latch.

Commonly used for connecting external reset buttons or PLC outputs.

7. Fuse protection

A fuse must be installed before the safety contact (recommended: fast melting 6A, slow melting 4A, gG 6A, or C-characteristic circuit breaker 4A/24V).

Auxiliary contacts also need protection (with the same parameters).

Parameter Setting and Debugging

1. Adjustment of response threshold (Uon)

There is a potentiometer on the equipment panel used to set the response values of two channels simultaneously (the range depends on the model).

Factory default: Rotate counterclockwise to the bottom (minimum sensitivity).

Setup steps:

Ensure that the motor is in a completely stationary state (preferably just a few seconds after shutdown).

Rotate the potentiometer counterclockwise to the bottom, and the "CH.1 IN" and "CH.2 IN" LEDs should not light up (voltage below threshold).

Slowly rotate the potentiometer clockwise until these two LEDs just light up. The threshold set at this time is slightly higher than the current residual voltage of the motor.

Verification: Start the motor and then stop it, observe whether the LED lights up again after stopping. If restored, the settings are correct.

Suggestion: Seal the potentiometer with the provided label to prevent accidental adjustment.

Important warning: Static detection is only effective when the motor is powered off (the power circuit is completely disconnected) and there is no external excitation. If the frequency converter has not yet output inhibit, or if the motor is in position control mode (with excitation current still present), PSWZ X1P cannot detect stillness.

2. Release value (Uoff)

Fixed at twice the response value (Uoff=2 × Uon), with hysteresis characteristics. This ensures that the safety contacts are reliably disconnected when the voltage rises during the motor start-up process.

3. Simultaneous monitoring time (tg)

Maximum of 7 seconds. When the motor stops, the voltage of both channels must be lower than the response value within 7 seconds at the same time, otherwise the "FAULT" LED will be triggered and locked.

This time is not adjustable, but it is sufficient for most motors.

Application example: Static monitoring with star delta starter

The manual provides a typical application (see figure on page 15). This example demonstrates how to integrate PSWZ X1P in the star delta startup circuit.

Circuit composition:

SO: Emergency stop switch (off switch)

S1: Start button

S2/S4: Safety door switch (series)

S3: Release button (for confirmation before startup)

S5: Reset button (connected to RESET input)

K1: Star/Triangle Control Relay

K2: Main contactor

K3: Triangle contactor

K4: Star contactor

H: Fault indicator light (connected to auxiliary contacts 41-42)

Key wiring:

The safety contacts 13-14 and 23-24 of PSWZ X1P are connected in series to the control circuit of the main contactor K2.

The feedback loop Y1-Y2 is connected in series with the normally closed auxiliary contact of K2 (or multiple contactors are connected in series to ensure that the feedback loop is disconnected when any contactor is stuck).

The measurement input terminals L1, L2, and L3 are directly connected to the U, V, and W terminals of the motor (downstream of the contactor and not affected by contactor switching).

Operation timing:

Close the safety door and the emergency stop is not activated. Press and release S3, and the feedback loop will close (due to K2 being disconnected).

When the static condition is met (the motor is not running), the "OUTPUT" LED lights up and the safety contact is closed.

Press the start button S1 and K2 to engage, and the motor will start in a star (or direct) manner.

After the motor runs, the voltage measured by PSWZ X1P is greater than Uoff, and the safety contact immediately opens (with a delay of less than 170ms), causing K2 to lose power. This action is not for power outage, but for quick disconnection in case of dangerous situations. But the external contactor control is used in this application, and the safety contacts of PSWZ X1P are only for monitoring purposes? In fact, the correct usage is that the safety contacts of PSWZ X1P should be connected in series in the self-locking path of K2 coil circuit, so that once the voltage exceeds the limit after the motor starts, the safety contacts will disconnect and K2 will be immediately released. This provides an anti accidental restart function.

When stopping normally, press the stop button, release K2, and the motor will run with inertia.

When the speed drops to zero, the residual magnetic voltage is lower than Uon, and both channels meet the conditions within 7 seconds, the PSWZ X1P closes the safety contacts again, allowing the next start.

Attention: During the star delta switching process, the measurement line must be connected to the motor terminal, not the contactor input terminal, otherwise the measurement signal will be lost at the moment of switching.

Troubleshooting and Common Problems

The PSWZ X1P provides status and fault indication through the front LED. The following are typical fault phenomena and their solutions.

Possible causes and solutions for LED status

POWER does not light up and there is no power supply/wrong power connection/fuse burnt out/internal damage. Check the voltage of A1 and A2 and the external fuse. Confirm that the voltage is within the rated range (24-240V AC/DC).

POWER is on, but CH.1 IN and CH.2 IN are not on, and the motor has come to a standstill. The response threshold is set too low (too much counterclockwise) or the measurement circuit is open. Adjust the potentiometer clockwise until the LED lights up. Check if the wiring of L1, L2, and L3 is broken or has poor contact.

In CH.1 IN/CH.2 IN, only one bright single channel voltage is below the threshold, while the other channel is above the threshold (possibly due to motor rotation causing phase voltage imbalance). Check if the motor wiring is missing phase. Measure the voltage of L1-L3 and L2-L3 in millivolt range using a multimeter (when the motor is stationary). If the difference is too large, it may be due to asymmetric residual magnetism of the motor, and it is necessary to reduce sensitivity or contact the manufacturer.

**OUTPUT is not lit, but both input LEDs are lit * * Feedback loop Y1-Y2 is not closed. Check if the external contactor normally closed auxiliary contact is connected. Temporary short circuit Y1-Y2 test (for diagnostic purposes only, cannot be permanently short circuited).

Press the reset button (to give RESET a high-low pulse) when the FAILT LED lights up at the same time or when the single channel voltage drops beyond the tolerance. If it repeatedly occurs, check whether the motor has completely stopped within 7 seconds (such as due to excessive inertia) or if there is poor contact in the measurement circuit.

The safety contact cannot be closed, even if the OUTPUT lights up and the relay contact is mechanically faulty or the welding power is cut off, manually test the contact resistance. If it doesn't work, replace the device.

During motor operation, if the safety contacts are not disconnected and the measured voltage does not reach Uoff (possibly due to low motor voltage), check if the rated voltage of the motor matches the actual power supply. The minimum measured voltage for PSWZ X1P is 0V, but the voltage must be greater than 2 × Uon during startup. If the motor is small, the residual voltage may always be lower than Uoff, causing the safety contacts to fail to operate. Solution: Choose a low threshold model.

Weekly mandatory testing (compliant with safety standards):

According to the manual, the following tests must be performed at least once a week:

Start the motor and confirm that all LEDs (except POWER) are turned off and the safety contacts are disconnected (measured with a multimeter 13-14).

Stop the motor.

Observe whether the CH.1 IN, CH.2 IN, and OUTPUT lights up again after the motor shaft is completely stationary. If it is not restored, it indicates that the static threshold is set improperly or there is abnormal residual magnetism in the motor.

Common Misunderstandings Clarification:

Misconception 1: PSWZ X1P can be used for speed monitoring. In fact, it can only distinguish between "rotation" and "stillness" and cannot measure specific rotational speeds.

Misconception 2: The output end of the frequency converter can be directly measured. Sure, but it is necessary to ensure that the inverter completely shuts off the output (i.e. the inverter pulse is blocked), otherwise high-frequency interference and high voltage may occur, which may damage the measurement circuit.

Misconception 3: Auxiliary contacts 41-42 can be used for safety interlocking. Error, it is only used for indication and does not guarantee safety performance.

Maintenance and lifespan

Relay mechanical lifespan: 10000000 cycles. But the electrical lifespan depends on the load current and voltage. Reference service life chart (page 33):

Under AC-1 (resistive load, 240V/6A), approximately 100000 cycles.

Under AC-15 (inductive load, 230V/3A), approximately 1000000 cycles.

Over 1000000 times under DC-1 (24V/6A).

Under DC-13 (24V/4A, inductive), approximately 300000 cycles.

Extend contact life: For inductive loads, arc extinguishing measures must be taken (such as RC absorption circuits, varistors, diodes, etc.). The DC coil needs to be connected in parallel with a freewheeling diode.

Regular inspection: Check the terminal screws for looseness (torque 0.5Nm) every six months and remove dust from the control cabinet.

Scrap disposal: Dispose of according to local electronic waste regulations, with no user replaceable fuses or batteries inside.

Interpretation of Safety Feature Data

To assist engineers in conducting safe calculations, PSWZ X1P provides the following values:

Standard parameter values

EN ISO 13849-1 Performance Level (PL) PL e

EN ISO 13849-1 Category Cat. 4

EN ISO 13849-1 PFH₀ [1/h] 6.23 × 10⁻⁹

EN ISO 13849-1 Task Time TM [year] 20

EN IEC 62061 SIL CL SIL 3

EN IEC 62061 PFH₀ [1/h] 6.23 × 10⁻⁹

The PFH value has taken into account the B10d value of the relay contacts and is effective under the load conditions given in the service life diagram. If the actual switching frequency is high, PFH will increase accordingly and needs to be recalculated.

The system security level depends on the architecture of the entire security loop, rather than individual components. It is recommended to use Pilz's PAScal software for circuit calculation.

Common application Q&A

Q1: Can PSWZ X1P be used for DC travel motors?

A: Sure, but only single-phase mode can be used (L1 connected to positive, L3 connected to negative, L2 suspended). At this point, there is only one measurement channel, and the security level will decrease (unable to reach Cat.4). For high demand applications, it is recommended to use three-phase motors.

Q2: If the motor has a mechanical brake, is static detection still necessary?

A: I need it. The brake can only keep the shaft from rotating, but there may still be residual magnetic voltage inside the motor. PSWZ X1P can detect this voltage to prevent misjudgment. Please make a static judgment after the brake is closed.

Q3: Can feedback loops use normally closed contacts of multiple contactors in series?

A: Okay. This can improve safety, as any contactor adhesion will cut off the feedback loop and prevent the safety output from closing. All contacts must be of the positive guided type for mechanical interlocking.

Q4: Can PSWZ X1P directly replace the old model PNOZ X1P?

A: Yes, it is. PSWZ X1P is a successor model of PNOZ X1P, with compatible functions, but the definition of connection terminals may be slightly adjusted. Please check the wiring diagram.