An optical amplifier arrangement is provided that includes an amplifier elements for measuring the gain applied to the total input power and a control unit adapted to determine the degree of variation of gain with wavelength, i. The pressure valve is configured to be closed when the pressure of the lubricating oil is less than a predetermined value, and to open when the pressure of the lubricating oil is greater than or equal to the predetermined value. The server may have a self signed or a trusted security certificate which may serve as a basis for issuing certificates to various clients. Further, the gated cell balancing converter provides a telemetry output voltage analog to an input cell voltage, eliminating the need for a separate cell voltage monitor. The brush portion has a plurality of strips and at least one layer of a fiber bundle.