M.C. Miller Cronos GPS Current Interrupter

Precision clock-timing even with an intermittent view of the GPS satellites.


M. C. Miller Cronos GPS Current Interrupter

45 Amp Model: Cat. # 12955
100 Amp Control Model: Cat. # 12950
100 Amp Relay: Cat. # 12965

M. C. Miller Sentinal Current Interrupter Companion
M. C. Miller Sentinal Current Interrupter Companion


  • Rugged M. C. Miller Co. design, highly reliable, easy to operate and very competitively-priced.
  • Precision clock-timing even with an intermittent view of the GPS satellites.
  • Two years of continuous (current interruption) operation on a single set of replaceable “D” cell batteries – no need to recharge the unit every few days
    Note: Although the batteries are the same physical size as regular “D” cell batteries, they are 3.6V, rather than the standard 1.5V “D” cells. The 3.6V “D” cells (19Ah capacity) are available from M. C. Miller (Cat. #BAT0064)
  • Easy to program via a PC or can “quick select” via the keypad
  • Available in 100A relay (external relay) and 40A relay (internal relay) models. Both relays are rated at 120V AC/DC
  • Solid-state (non-polarity dependent) relay – no unit orientation or polarity concerns
  • Only 1mV dropped across the relay per Amp – both small and large currents can be interrupted
  • Fully-automated current-interruption programs can be started in the field with the push of a single button.

When multiple current interrupters are employed on a pipeline, their internal clocks must be synchronized in order to guarantee “in-phase” current switching so that accurate instant-off potentials can be recorded.

With “non-GPS” current-interrupter units, in order to achieve (initial) clock synchronization, all participating units have to be brought together in one place. Furthermore, because of clock-drift due to local temperature variations and other effects, the clocks in the participating units can quite quickly drift out of synchronization, which leads to “out-of-phase” current waveforms.

The ideal scenario is one in which current-interrupter units can be left in the field for indefinite periods of time (with no external power source required) and their internal clocks will always be synchronized with each other during critical time periods, such as periods of repetitive current interruption (current cycling periods).

Our GPS Current-Interrupter (the Cronos unit) satisfies both of these “ideal-case” requirements.

The Cronos unit does not require an external power supply and it can run applications for years at a time using an internal battery power source. This is possible due to the advanced design of the Cronos unit which results in extremely-low power consumption, even when the unit is tracking GPS satellites.


Maximum Current:

100 Amps at 120V (12,000 watts) external relay
40 Amps at 120V (4,800 watts) internal relay

Maximum Working Voltage:

170V DC (either polarity), 120Vrms (50/60Hz).

Voltage Drop:

1mV per Amp Suitable for interrupting low Voltage bonds and anodes.

Overload Protection:

75kW(10/100?s); 500kW(8/20?s) 1.2kA peak @ clamp voltage. Auto thermal shutdown at 105°C.

Isolation to ground:

2,000 Volts

Setup Options:
  • On/Off 0.1 to 99 sec. 0.1 sec increments
  • Start and stop date and time
  • Begin cycle with relay open or closed
  • Close relay at end of work day
  • Start cycle at beginning of work day
  • Switching offsets ±500ms (both On-to-Off and Off-to-On) — allows for use of other relay types.
Power Consumption:
  • Runs on 2 “D” Cell batteries (3.6V, 19Ah)
  • Battery-life depends on programmable settings — 2 years continuous operation typical on default settings.
Time Standards:

UTC (default) or GPS; Synchronization @ 00.00 (default) or @ start time; Local–Offset; user defined to ensure consistency

Clock/Interruption Accuracy:
  • 1ms max. deviation with satellites in view
  • 0.5 ms per hour without satellites in view
  • Reacquires precision time when satellites return to view
Temperature compensated range:

-40°C to +85°C.

Temperature Range:
  • Relay Operation: -40°C to +85°C
  • LCD Operation: -20°C to +70°C
Multiple Unit Programming:

Cronos PC software allows personal settings to be created and saved for future download to Cronos units, or a “master” Cronos unit can be used to automatically program other Cronos units.

  • 40A Model: 9″L, 11″W, 6″D (15.4 lbs)
  • 100A Model:
    Control Unit: 9″L, 11″W, 3″D (5.6 lbs.)
    Relay Unit: 13.5″L, 7″W, 4″D (19.4 lbs.)
Ships with the following:
  • 6 feet of ultra flexible #2 cable
  • Windows setup software
  • PC to Cronos RS-232 cable

Additional information


45 Amp Model, 100 Amp Control Model, 100 Amp Relay Model


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