FAQ

1.
Q: Round Axis
A: In TWK encoder is no round axis integrated. If the customer sets e.g. number of turns to 24, then the encoder autonomously sets internal next higher 2^n number of turns available in the measuring range. The mismatch to the configured setup in the config tool and encoder will be detected by checksum issues. Explanation of behavior see in the manual on page 44 or chapter 6.1.2 Description of the Absolute Encoder Parameter.

2.
Q: How to set Preset value?
A: Within the control word the bit must be set to activate the preset value. In the "data stream" the control word, preset value and F-data must be sent. Be aware that the control bit must be set back to 0, because only with the rising slope of the bit control flag the preset value is overtaken.

3.
Q: How to use Device Address
A: The number of the device address must match in the device name with the setting under F- parameter with F_Dest_Add. See here also hints in the manual chapter 4.2.5.1.

4.
Q: Why do I see just 0 Values in the Watch Window?
A: If the general integration of the encoder in the project was successful like naming, address and so on and the LEDs indicate a green status, but you get only 0 values in the watch window, then you have not used Process Data Input values from the safety encoder in the safety program. Only when the encoder is used in F-program (safety related), then the Profisafe communication is started with the encoder. This explains why you see 0 values, when the process values like position or velocity are not used in the safety program. Furthermore, in the TIA portal version you can use a so called acknowledge global flag for automatic re-insertion of all failed devices.

5.
Q: Why there are Just 0 Values as Process Value?
A: The same behavior as above can be also observed when the wrong device class is selected like TIA instead of NON-TIA from the device type. Please check type label information and selected device type in the project tool.

6.
Q: What is the capability of ABB SM560 safety PLC?
A: This type of PLC just supports 16-bit data safety consistency and NON-TIA version shall be used.

7.
Q: How to use Profisafe Encoder with Draw Wire?
A: It is strongly not recommended to use a standard Profisafe encoder together with a drawer wire sensor. Root cause for this restriction: The torque needed to drive the encoder shaft is quite high and the spring inside the draw sensor may be blocked. This failure case is not allowed for a safety device.

8.
Q: Which material should be used for salt water?
A: V4A stainless steel version is recommended for salt water.

9.
Q: On which resolution velocity calculation is based on?
A: The velocity is always based on the raw value and not on the scaled one and additional always based on 12 bit Single-Turn resolution, even when a 13-bit resolution type as single-turn is used!!
For low speed you need to consider linearity of 0.2% per revolution and quantization issue of the resolution. Monitoring of both channels is based on position value and velocity calculated on one of both.
Integration time takes a real position value difference at logging time. Each 1 ms a new velocity value is calculated.
Example: integration time 1 s. That means the encoder stores 1000 position values and is calculating a position difference between 1 sec.

10.
Q: What does the error message: Internal communication error TPS-1 means?
A: This message occurs very seldom as I heard from TWK. Maybe it is related to a soldering problem on the PCB which interrupts the communication between their ProfiNet controller and their main controller or it is related to EMC issues in the installation. Regarding EMC all our standard measures should be considered as usual as shielded cables, good electrical connection between encoder flange and machine/potential earth, no ground loops, ...

11.
Q: Is it possible to use Profisafe encoder with other PLC manufacturers than SIEMENS?
A: This is in principle possible as Profisafe is a generic interface and not binded to one PLC manufacturer brand. BUT you need to check if 32-bit safety values can be handled as one consistent value or not. In case 32 Bit consistent value can be handled, then use TIA version otherwise NON-TIA version.