Laboratory time consistency solution-Part1

The laboratory is an almost ideal working environment, such as standard atmospheric pressure, constant temperature, clean room, etc., so that changes in things are minimized by the impact of the environment, and then discover the law of everything.

But LABS often overlook an important physical factor: time, one of the seven fundamental physical quantities. As expressed in Segal's Law, a person who has only one table can determine the current time; If there are two tables, then he will not be able to determine the current time. Under the unified time system, we can better determine the reliability of the law of change. The higher the accuracy of time synchronization, the clearer the law of change.

The more we see things from a variety of angles, the more LABS need to work on the same frequency or in sync. For example, the space laboratory requires multiple space payloads to work synchronously at the same frequency, and the clock is required to reach US-level synchronization; The communication laboratory needs to verify the reliability of the communication, the communication bandwidth of the terminal has subdivision requirements, the frequency accuracy is required to meet the accuracy requirements of at least 1E-9, and the clock synchronization is also required to reach the us level. The synchronization requirements of many laboratories in chemical medicine for experimental event records should reach ms level; High speed event capture synchronization needs to reach 1us level... The popularity of distributed laboratories highlights the society's higher requirements for time synchronization.

Recently, as a proof of potential and a first step toward a functional quantum network, a research team at Illinois Fast Quantum Networks (IEQNET) successfully deployed a long-distance quantum network using local fiber between two U.S. Department of Energy (DOE) laboratories. The experiment marks the first time quantum-encoded photons (particles that transmit quantum information) and classical signals have been transmitted simultaneously over long distances at unprecedented levels of synchronization, with clock synchronization reaching an astonishing level of better than 5ps.

What are the time demands of the laboratory?

On the whole, there are three requirements for clock synchronization in the laboratory: working at the same frequency; Control synchronization; Event records are synchronized.

◾ work in the same frequency

Working at the same frequency means working at the same frequency or with the same frequency accuracy. The same frequency work mainly uses the time-frequency 10M, 10.23M signal or other special frequency points as the reference frequency to work, so that multiple devices can achieve frequency synchronization, ensure the consistency of frequency accuracy, and make the working time sequence synchronous and stable.

◾ Control synchronization

Control synchronization refers to the need for multiple devices to control synchronization pulses, which is also a kind of time synchronization to a certain extent, and needs to be controlled according to the agreed trigger time.

◾ Synchronizes event records

Event record synchronization means that the terminal that records event information needs to synchronize time. For example, the computer can timestamp the event according to the accuracy of ms, marking the moment when the event information occurred, and the high-speed ePCI high-speed acquisition card also needs to realize the US-level timestamp record. Time synchronization is needed to record the cooperative event information of multiple devices. The inconsistency of time will cause the confusion and inefficiency of the event information record.

How to achieve time synchronization in the laboratory?

First of all, we need to understand the basic expression of Time, which mainly includes two parts: Second and time (year, month, day, minute and second information), that is, we often say 1PPS (Pulse Per Second) and TOD (Time of Date) information. The change of 1PPS time interval reflects the characteristics of frequency, and the accuracy of frequency can be calculated and adjusted by the change of 1PPS time interval to further achieve the same frequency.

Time synchronization means that the time giver transmits 1PPS and TOD information in different forms, and the time giver modifies the current time through the comparison and control of 1PPS and TOD.

At present, the mainstream time transmission methods are: 1PPS+TOD, IRIG-B(DC), IRIG-B(AC), E1, PTP, NTP, optical fiber and satellite receiver. According to the direction of timing information transmission, it can be divided into one-way time synchronization and two-way time synchronization. The unidirectional time synchronization method includes 1PPT+TOD, IRIG-B(DC), IRIG-B(AC) and satellite receiver; Bidirectional time synchronization methods include E1, PTP, NTP, fiber optic time synchronization, satellite covision and satellite bidirectional.

Unidirectional time synchronization method take the IRIG-B code as an example, IRIG is short for the American range instrument group, IRIG time standard is divided into parallel time code format and serial time code format, because the parallel format transmission distance is close, and is binary, so the application of parallel time code is far less than the serial time code. Serial time codes are available in six formats: A, B, D, E, G, and H. Their main difference is the time code frame rate is different, IRIG-B is one of the type B code, because the B code frame rate is 1 frame /s, the most in line with the applicable habits, so the B code is the most widely used.

Each pulse in the B-code time format is called a code element, the punctual reference point of the code element is its pulse front, the repetition rate of the code element is called the code rate, and the code rate of the B-code is 100ps. The code element contains the year, month, day, hour, minute and second information, and also has the code element of the standard second position. Its time synchronization accuracy can reach tens of nanoseconds. In addition to the transmission function of time information, B code also reserves a group of code elements for control functions.

Two-way time synchronization is a kind of master/slave synchronization mode, which calculates the transmission delay and time compensation amount through the time of sending and receiving the information of the master/slave interaction, and further realizes the time compensation. The accuracy of the time stamp of the information and the symmetry of the link round trip are important factors affecting the two-way time synchronization. For example, compared with NTP, PTP is a hardware timestamp marking method, which is higher than the software timestamp accuracy of NTP, so the synchronization accuracy is much higher. Later, we will also carry out a thematic discussion to introduce the characteristics and applications of these time transfer methods.

The time synchronization of the laboratory is to unify the time of different categories of equipment by these transmission methods.

What constitutes the time synchronization service system of the laboratory?

The laboratory's time synchronization service system can be divided into four parts: GNSS satellite traceability, time-frequency unification, time-frequency measurement and time-frequency transmission. It addresses four major questions: Where does time come from? How to distribute multiple time transmission modes uniformly? How much time is left? Where did the time go?

◾ Where does the time come from?

The time mentioned here refers to UTC time (Coordinated Universal Time), which is the unified time of the world. The source of UTC time can provide us with two aspects of information, one is the standard time and the other is the standard frequency. This provides a reference for us to choose the time source, if we have a demand for standard time and standard frequency, then we have to choose the equipment with UTC time acquisition function as the laboratory time source.

After years of painstaking research, California Triangle has derived a large number of mature products based on satellite timing technology. Such as CT2500 multi-function time-frequency fusion platform, CT3000 high-end NTP time server, CT7300 IEEE1588 high-performance time system equipment, etc. Can meet a variety of laboratory time work.