EPOS4: Hall sensor error (0x7388)?

Topic:

• What causes a "Hall sensor error" (0x7388) reported by an EPOS4?
• What should be checked in case of the "Hall sensor error" state?

Solution:

The "EPOS4 Firmware Specification" lists the following possible causes in case of an "Hall sensor error" (-> error code 0x7388):

Precondition for any error assessment:

For the evaluation of error states of the motor and especially its sensors (e.g. Hall sensors or encoders), it is mandatory that a motor and its sensors are actually connected! 

If no motor or sensor is connected, depending on the configuration of the EPOS, error messages can occur immediately after power on. If, for example, an EC motor is configured but no Hall sensors are connected, the controller reports a "Hall sensor error". It is not possible for the EPOS to detect whether the Hall sensors or their wiring is defective or whether no motor is connected at all. It is assumed for operation that a motor and its sensors are connected. The error messages are also based on this assumption.

Make sure that a motor and sensors are connected before looking for one of the other possible causes in case of a sensor error.

The most frequent root causes:

If there is a "Hall sensor error" (code: 0x7388) present, this is almost ever due to a defect of one or more Hall sensors of the motor.

Another observed cause of an "Hall sensor error" state are loose contacts or damaged wires inside the Hall sensor cable or by a bad crimp or screw terminal connection. In the case of a loose contact, the error message might just occur sporadically when the cable is moved or vibration is present. 

If the error occurs only sporadically during motor operation and especially during rapid acceleration or deceleration or high motor currents (= high motor load), a signal disturbance on the Hall sensor cables caused by the motor cable, so-called EMI (= Electromagnetic interference), can also be the cause.

Almost never is the EPOS4 the root cause of the error state. The EPOS4 just reports the problem. Defect Hall sensor inputs of the EPOS4 or even a software malfunction can almost always be excluded in practice. 

Due to the mentioned most frequent error causes, the correct function of the Hall sensors and the wiring should always be checked first.

In the event of suspected problems with EMI signal disturbance, it is essential to follow the general wiring instructions and to keep motor phase lines (i.e. the winding wires) clearly separated from the Hall sensor lines. 

General wiring recommendations:

Do not use just one common cable for Hall sensor signals wires (incl. 5V and GND) and the motor winding phase wires, especially not in case of powerful motors or any cable extensions.

• Ensure that Hall sensors wires (incl. its 5V and GND) are clearly separated in their own cable and kept away from the motor's phase wires to avoid any risk of EMI.
• The three motor winding phase wires should be "packed" into one common cable with a shielding. The shielding has to be connected to Earth by a broad contact.
• Please find more recommendations about wiring details by this Support Center document:
  -> Measures in case of long cables

Possible tests to check the Hall sensors and EPOS4

The Hall sensor signals can be checked by the power stage in "Disable" state (or just connecting power by EPOS4's X2 but not X1) and turning the motor shaft very slowly manually. Unfortunately, this test option is not available for engine combinations with multi-stage or high-ratio transmissions due to transmission self-locking

There are two different ways how the Hall sensor signals and processing by the EPOS4 can be checked if it is possible to move the motor shaft.

1.) Test by an oscilloscope

• There is an oscilloscope with at least three channels required.
• Attach signal probe heads in between each Hall sensor output of the motor and the Hall sensor's common GND.
• Turn the motor (or gear) shaft very slowly by hand. The following Hall sensor pattern sequence (like present by maxon's catalog) should be present then:
  
• Remarks:
  • If there is a multi-pole pair motor (e.g. "EC-flat", "EC-i", "EC-4pole") in use, the complete sequence above will be present multiple times according to the number of pole pairs within one mechanical turn of the motor shaft.
    Example:
    In case of an "EC-i 52" with 8 pole pairs, the sequence will be present eight times per one mechanical turn of the motor shaft.
  • If there is a gear present, the gear ratio also has to be taken into account to determine the number of sequences per one turn of the gear shaft.
    Example:
    "EC-i 52" with 8 pole pairs and a 12:1 gear
    => The sequence will be present 96 times per one mechanical turn of the gear shaft.
• A signal voltage in between 4.5 ... 5V will be typically measured in case the Hall sensors are supplied by the EPOS4's 5V output.
  • Any pulse voltage measurement above 2.0V is already o.k. and rated as a "High" signal state by the EPOS4. 
• Check the signals directly at the motor's Hall sensor output and at the end of the cable connected to the EPOS4 if possible. It can be identified then if actually the motor's Hall sensor signals are not o.k. or there might be some broken or loose wire or contact by the cable present.
  
  
• Analysis:
  • If one (or more) Hall sensors report a permanent voltage of 0V or permanently above 2V while the motor shaft is turned, the corresponding Hall sensor(s) are damaged. In case of permanent 0V also a cable break or bad connector contact could be present.
  • If the Hall sensor signals and signal sequence(!) on the motor side are correct, it can be assumed that the Hall sensors are working properly.
  • If the Hall sensor signals are no longer correct at the EPOS4's cable end, a cable defect must be considered.
  • If the signals and level changes are present of each Hall sensor at the end of the cable, but the signal sequence is not correct, the Hall sensor signal lines have probably been interchanged at the connector.
  • If the Hall sensor signals and signal sequence are correct at the cable end at the EPOS4 connection, there may be a defect of the EPOS4's Hall sensor inputs present. If the error state just happens during motor operation, some EMI can be also still a possible root cause. 

2.) Test by EPOS Studio's "Data recorder"

If the Hall sensor signals and wiring seem to be o.k. based on the voltage measured by an oscilloscope, the signals received by the EPOS4 can be checked by EPOS Studio's "Data recorder" to determine if the EPOS4's Hall sensor inputs might be damaged and causing the error message.

• Check the Hall sensor signal states by selecting the following EPOS Studio "Data recorder" channels:
  ​
  Remark:
  Depending how fast you move the motor shaft, the "Sampling Time" has to be adjusted to ensure that any state change of the "Digital hall sensor pattern" is captured.
  
  
• "Disable" the power stage and move the motor (or gear) shaft slowly by hand. The recorded "Digital hall sensor pattern" values must vary in between 1 ... 6 only. Any other value (e.g. 0 or 7) means that there is some malfunction by the Hall sensor signals present!
  
  
• Right click in the stopped graphics and activate the "Cursor" to check the value at each state more easily. The sequence of the "Digital hall sensor pattern" values should look like this in a repetitive way (depending on the direction of rotation vice versa):
  5 -> 1 -> 3 -> 2 -> 6 -> 4 -> 5 -> 1 -> 3 -> 2 -> 6 -> 4 -> ....
  The "Position actual value" will also change depending on the direction of rotation.
  
  
• Please find a screenshot of EPOS Studio's "Data Recorder" based on an EC-motor (1-pole pair) and the Hall sensor also in use for position data processing (i.e. no encoder present):
  
  Remarks:
  • In the attachment you will find the recording file "Sample-Hallsensor-Recording.csv". This file can be loaded into the EPOS Studio "Data Recorder". By means of the contained graphic data it can be checked with the cursor how the signal sequence of the "Digital hall sensor pattern" values should look like. The different period length of the states is caused by the less continuous manual movement of the motor shaft and is not relevant.
  • If a multipole motor or gearbox is used, the data sequence occurs several times per revolution of the motor shaft. The shaft must therefore be rotated very slowly to capture all signal states of one sequence.
    
• Analysis:
  If the data values of the "Digital hall sensor pattern" or their sequence is not correct, a defect of one or more Hall sensors or a wiring error is causing the error state. In very rare cases a defect of the EPOS4 Hall sensor inputs or 5V supply can also not be excluded.

  • If a "Digital hall sensor pattern" value of 0 or 7 occurs sporadically, it is very likely that a Hall sensor is not working or there is possibly a defect by an Hall sensor wire.

  • If a "Digital hall sensor pattern" value of 0 or 7 occurs permanently, there is usually a defect of all Hall sensors present. It is also possible that the power supply (5V, GND) of the Hall sensors (-> wiring?) is not o.k. 

  • If all Hall sensor signals are correctly present and change when the motor shaft is rotated, but the value sequence of the "Digital hall sensor pattern" is not correct, the connection pins of the Hall sensor signals (H1, H2, H3) have probably been interchanged. In this case the pin assignment and wire colors should be checked again carefully.

Conclusion & possible actions

• In case of an "Hall sensor error" (0x7388) this is almost always caused by some damaged Hall sensors. It would be also possible that an EPOS4 Hall sensor input is damaged but this has not been the case for all returned and tested EPOS4s up to now. Therefore the correct signals of the motor's Hall sensors have to be checked first of all. 
• The Hall sensor's output voltage measurement by an oscilloscope (-> 1.) should clarify if the Hall sensors (or wiring) are damaged and the EPOS4 error message is caused by this.
  • Hall sensors cannot be repaired or replaced. This means that in case of a motor combination (with a gear and encoder) only the complete motor can be replaced by maxon's "Service and Repair Center" but no single Hall sensors. If replacing the motor and keeping the gear and encoder is worth the effort (and cost) from the commercial point of view depends how long the gear had been already in use.
  • Sometimes it is faster and even more efficient to directly replace a motor combination which had been already in use for a long period of time by a complete new motor combination.
• The test by EPOS Studio's "Data Recorder" (-> 2.) can just clarify if the Hall sensors are present and can be processed properly by the EPOS4. If an oscilloscope's measurement (-> 1.) has previously confirmed that the Hall sensor signals and wiring is o.k., it has to be assumed that EPOS4's Hall sensor inputs might be damaged if the "Hall sensor error" occurs even if the power stage is in "Disable" state (i.e. no EMI can impact the Hall sensor signals' quality). 
  • If the EPOS4 seems to be damaged, this can be repaired by maxon's "Service and Repair Center".
• Please contact your local maxon point of contact to clarify the next possible actions in case of damaged Hall sensors or a damaged EPOS4. maxon's local sales organization or your local maxon partner will provide a return case number and process the return from maxon's local site to maxon's "Service and Repair Center".

Additional notes:

EC-motor operation without Hall sensors?

The Hall sensors are required to determine motor shaft position for applying the voltage properly for winding commutation. The Hall sensors are even required if there is an incremental encoder present to determine the motor shaft position initially at start-up of the motor after EPOS4's power-on or a reset. You can find some more information about this topic by the following linked Support Center document:
-> EPOS4: Sensors & start procedure of sinusoidal commutation.

It is just possible to operate an EC-motor without Hall sensors by an EPOS4 if there is a SSI absolute encoder mounted on the motor shaft. The motor shaft position and the correct motor commutation can be identified based on the SSI's absolute single-turn data and its defined mounting position (-> commutation offset value) without the need for Hall sensors.

Cross reference:

• Please find a summary of all EPOS4 error states and possible root causes by chapter "7 Error Handling" of the "EPOS4 Firmware Specification".
• Please find some general notes how to retrieve the error code in case of an EtherCAT slave (e.g. EPOS4 EtherCAT product type) by the following linked Support Center document:
  -> EPOS4 / IDX EtherCAT: Which object holds the error codes?