The ES-151U is a master clock switcher. Master clock switchers are typically used with a primary master clock (‘A’) and a secondary master clock (‘B’). Master clock switchers provide a convenient way of switching to the secondary master clock if a problem develops with the primary master clock. The Master clock switcher monitors one or more of the ‘A’ inputs and when a fault is detected, it switches all of the outputs from the ‘A’ inputs to the ‘B’ inputs. The ES-151U monitors IRIG-A, B, or E time codes, in either Modulated or TTL (DCLS) form. Four front panel LEDs light to indicate when valid time code is provided. These LEDs are TTL ‘A’ status, TTL ‘B’ status, MOD ‘A’ status and MOD ‘B’ status. When these LEDs are green, valid time code is being supplied to the unit. When these LEDs are red, no time code or invalid time code is being provided to the unit. The ‘A’ and ‘B’ Active LEDs indicate which set of inputs are being used for the purpose of switching the outputs. The ES-151U can monitor the TTL ‘A’ Input, the Modulated ‘A’ Input or both at the same time. The Code pushbutton allows the user to select which inputs to monitor. If a fault is detected, the unit switches all outputs from the ‘A’ inputs to the ‘B’ inputs. The Mode pushbutton allows the user to put the ES-151U in one of four modes: force all of the outputs to use the ‘A’ inputs, force all of the outputs to use the ‘B’ inputs, Auto and Trip. If the unit is being forced to use the ‘A’ or ‘B’ inputs, neither the Trip or Auto LEDs are lit. In Auto mode, the Auto LED is lit. If a fault is detected, the outputs switch over to the ‘B’ inputs. If the TTL ‘A’ input, the MOD ‘A’ input or both (depending on which codes the unit is set to monitor) are determined to be valid after the fault has been detected, the outputs automatically switch back to the ‘A’ inputs. In Trip mode, the Trip LED is lit. The outputs do not switch back to the ‘A’ inputs until the Reset button is pushed.

All time code connectors are BNC. Three sets of passive switched BNC's are also provided, along with 5 sets of solder terminal I/O's located on the rear DB-25 connector.

Options clear, DPS, NET and UL are available. Option DPS provides dual power supplies for the ES-151U. If one power supply fails, the other keeps the ES-151U operating normally. Option NET allows the user to control and monitor the status of the ES-151U via a web page interface.

The ES-150U operates in the same way, except it uses ESE