Semight-SUPPORT-FAQ-Semight Instruments

Q&A

Common Problem

Product category

？Q

Why does the eye pattern test deteriorate when the bit error test instrument is replaced?

A

After confirming that the test environment is OK, it is necessary to adjust the pre emphasis according to the environment and the product, as shown in the following figure.
？Q

Use the self-contained trig of the bit error test instrument. After replacing the channel of the bit error test instrument with the test eye chart, the trig cannot be locked, and the eye chart test fails.

A

The electric self loop of the error meter confirms whether the signal of the error meter is normal. If the error meter trig is used, confirm whether the corresponding channel selected by the trig is correct.
？Q

Will the polarity of the bit error test instrument be reversed?

A

MBT5210 BERT: opposite polarity, no connection, single ended connection, slightly poor sensitivity.
PAM4 BERT: NRZ mode polarity is opposite and pass, pam4 mode polarity is opposite and pass.
？Q

What is the principle that there is still error code after the error code test instrument is corrected? What is the general reason?

A

Judging from the distribution, the channel has burst errors, so the error after correction is > 0, because the symbol err distribution exceeds the theoretical error correction ability of FEC (< 15) The bit error rate of e-9 is the average bit error rate. It is not easy to see sporadic burst errors hidden in it.
FEC error correction capability analysis: the following figure shows the extreme scenarios of the above two cases The error distribution of both figures can meet the error rate of 0 after FEC correction. However, if there is one more column in the figure above and one more bit in the figure below, FEC cannot be corrected.

Causes of sporadic large errors: channel crosstalk, link loss, DFE equalization processing, etc. may all cause sudden errors. At a certain time, on some data packets, there are some burst errors beyond the ability of the error correction algorithm. It can be distributed continuously in a large area in a data packet at a moment, or it can appear randomly in every symbol, but the number of occurrences is enough All these will lead to unrecoverable data packets at this moment.
？Q

What is the meaning of msblsb? What's the relationship with TX ±?

A

High bit MSB, low bit LSB, MSB / LSB correspond to digital bit coding.
TX ± refers to the positive and negative poles of the differential signal, and corresponds to analog comments.
For each PAM4 symbol (2bits), the method of converting digital code into analog level is MSB + LSB / 2 to achieve output changes of four levels.
？Q

Does optical power meter OPM support automatic coupling?

A

It won't support.
？Q

Does optical power meter OPM and VOA support GPIB communication? Or can I go through visa?

A

No, only USB & network port communication is supported.
？Q

Why can optical power meter OPM test burst power?

A

No, only intelligent continuous light can be tested.
？Q

Why is OPM power monitoring inaccurate?

A

(1): First check whether the end face of the optical fiber is dirty (you can check the state of the end face with the end face detector), and then clean the lower end face with a cleaning pen or a face tag.
(2): Check whether there is dirt on the lower PD end face (after unscrewing the adapter, clean the lower PD end face with some alcohol that is still stuck gently).

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