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Voltage sag often leads to interruption of industrial production processes, which brings huge economic losses to users. Taking measures from the user side is the main measure to mitigate the effects of voltage sag today. Reasonable evaluation of voltage sag immunity in industrial process is the premise of the degradation of governance. However, the current evaluation method needs to test the entire industrial process, which will cause economic losses to the users who conduct the test. Therefore, this test scheme has no practical evaluation value. This article is based on the relationship between equipment attributes and process physical attributes. Further link the equipment endurance ability with the industrial process endurance ability, through the test of single equipment to achieve the assessment of the entire industrial process endurance ability. At the same time, the case study of an industrial park shows the practicability and effectiveness of the scheme.

Two Cs fountains clocks have been built in NIM. NIM5 fountain clock has been reported to BIPM since 2014. The microwave synthesizer and computer control system of NIM5 had been modified recently. The Type-B uncertainty is 9×10-16, limited by the interferometric switch in the microwave chain. The new NIM6 fountain clock has been built and evaluated, the preliminary results are presented in the paper. With an ultra-stable microwave signal generated from an optical comb which locked to an ultra-stable laser, the frequency instability of NIM6 fountain clock reached $5 \times 10^-14$/$\tau^1/2$ at high density. The direct comparison of two fountain clocks has also been done, a relative frequency difference of $4.4 \times 10^{16}$ was obtained for 20 days averaging time, consistent with the total uncertainties of the two clocks.

An ultra-stable microwave down converted from the ultra-stable laser directly by an optical frequency comb (OFC) is built at the National Institute of Metrology China. The repetition rate (f r ) of OFC is stabilized by stabilizing the sum of the carrier envelope offset frequency (f ceo ) of OFC and the beating frequency between the ultra-stable laser (USL) and OFC. A current feedback with 30 kHz bandwidth and a piezoelectric transducer with 1 kHz bandwidth are applied for the frequency stabilization. The frequency jitter of the stabilized sum frequency is about 4 Hz. Though the counting of locked f r , the shifted frequency of the USL is about 2087 Hz/day. As the frequency jitter of the mixing frequency of f ceo and the beating frequency between this OFC and another USL is about 10Hz, the short time stability of f r is calculated to be about 5e-14. This ultra-stable microwave will be applied as the local oscillator for NIM5 Cs fountain to improve its shorter term instability.

We report the design of a new cesium fountain clock NIM6, which is under construction in NIM. Besides some improvements on the vacuum system, Ramsey cavity and microwave synthesizer to reduce the Type B uncertainty. Another major improvement on NIM6 is to collect more atoms from a MOT loading optical molasses and optical pumping to get a better signal to noise ratio at the detection. The atom distribution will be more uniform compared with a 2D MOT loading optical molasses, and the diameter of the cloud can be adjusted by the intensity and detuning of lights during the post cooling to keep the collisional-induced frequency shift low. The atom numbers can be further increased by a new de-pumping - optical pumping procedure to pump atoms to the |F=3, m F =0> clock state directly. With a new cryogenic sapphire oscillator (CSO) based frequency synthesizer, NIM6 is aiming to reach the quantum projection noise, thus leading to a reduced Type A uncertainty compared with NIM5.

The triggered-phase transient analyzer (TPTA) was developed in our laboratory recently. With TPTA, the phase transient of Mach-Zehnder interferometric switch which was used to reduce the microwave leakage was studied. From the measurement results, it seemed that there were some kinds of thermal effect in our interferometric switch. The TPTA has the ability to measure the phase variations of two pulsed microwaves with a fixed interval in one cycle. Therefore, after measuring the phase discontinuity between two switching on states in one fountain clock's cycle, the frequency uncertainty induced by interferometric switch was reported in this paper.

The caesium fountain primary frequency standard NIM5 has been developed at the National Institute of Metrology (NIM) of China. The NIM5 loads atoms in an optical molasses (OM) from the background Cs vapor directly. Atoms are then cooled to a temperature of about 2 μK and launched to a height of 81 cm. The fringes of the Ramsey pattern have a width of about 1 Hz. Stabilizing the 9.19 GHz microwave frequency to the centre of the central Ramsey fringe, a typical fractional frequency stability of 3×10 -13 (τ/s) -1/2 is obtained when running at high atom density, and a combined uncertainty, including Type A and B uncertainties is typically less than 1.6×10 -15 . The NIM5 operates for more than 300 days in a year with nearly continuous operation over 15 days. Comparisons of data among the NIM5 fountain clock and other 5 fountain frequency clocks were carried out in May, 2013 through Two-Way Satellite Time and Frequency Transfer (TWSTFT), also NIM5 was compared with UTC through UTC(NIM). The results demonstrated agreement within the stated uncertainties.

We are developing a new Cs fountain frequency standard in NIM, and shooting for the frequency uncertainty of a few parts in 1016. The new fountain will run in a lab with the temperature fluctuation of 0.3K, and no active temperature control system will be added outside the flight tube. Instead, an isothermal liner will be surrounded the flight tube. It is a special type of heat pipe, made of a thin layer of vacuum tube filled with pure water. The thermal conductivity of a glass isothermal liner is about 10 times higher than that of coppers. It also works like a low pass filter reducing the temperature fluctuations of the system. The advantage of using an isothermal liner is to make the temperature of the whole interrogation region more uniform and stable. With precision standard Pt thermometers measuring the temperatures of a few locations of the flight tube, the average temperature uncertainty is less than 50 mK. The frequency shift due to the blackbody radiation can be calculated, and the relative frequency shift due to black body radiation can reach down to 7.2E-17 of this new fountain clock. Key words: Fountain clock, blackbody radiation, heat pipe.

We report the preliminary laboratory experiments on a 9.2 GHz frequency signal transfer through a 10 km commercial 1550 nm fiber spool in NIM. Theory analysis shows that increasing modulation frequency can significantly enhance the detecting sensitivity of fiber noise, as well as the sensitivity of compensating the noise. Because of the phase shift induced by fiber dispersion between the two first sidebands of EO (electro-optical) modulated optical carrier, beat signal between them, which can not be detected without phase shift, can be used as transferred signal with double modulation frequency. With actively canceling the noise induced by fiber, we have obtained a stability of about 8E-16/1000s up to now only with slow loop servo actuating by MDL (Motor Drove Delay Line).

The NIM4 atomic fountain clock has been operating since August 2003. We in this paper report the experiments certifying its stability of 8E-13//spl tau//sup 1/2/, reproducibility of 5E-15, and present results of the first evaluation for its systematic frequency correction with an uncertainty of 8.5 E-15 during September to December 2003.