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Why is the fan on the Counter still operating after turning the power off?

Removing the power from the internal Time Base, even for a short length of time, requires the Time Base oscillator to go through its power on cycle fluctuation (retrace) before coming to rest at a stable frequency. For this reason, even when the power is off, the counter remains in a standby mode to prevent the oscillations that happen every time power is cycled. The only way to completely turn the counter off is to remove the AC power source.

The counter has three operating modes, as follows:

ON - Power is applied and the ON/OFF switch is set to ON. Everything on the counter is operational, like the measurement circuitry, display, etc. The fan is on.

STANDBY - Power is applied and the ON/OFF switch is set to OFF. The power to the Time Base remains and the fan stays on. This is to keep the Time Base oscillator stable. The rest of the counter is not operational.

OFF - Power is removed from the counter. Nothing is operational including the fan. The Time Base needs time to stabilize after applying power to the counter.

Leaving the counter ON reduces the risk of accidentally unplugging the counter. This occurs more likely when placing the counter in the STANDBY mode. However, both the ON and STANDBY modes operates the fan to maintain long-term measurement reliability.

The specified aging rate for the Time Base assumes a stable Time Base oscillator. Each time the power is removed from the counter, the aging rate must start over from the daily aging rate. Dependent on the counter, it can take the counter up to 30 days after re-applying power to meet the specified aging rate. This is true even if the counter is maintained at a steady temperature of 25 degrees C. Unplugged the counter and cycling power creates a "surge”"on the Time Base oscillator that can take 30 days for it to stabilize.

Agilent strongly recommends keeping the counter in a location where it can remain powered; operating between ON and STANDBY mode ensures the most stable operation of the Time Base crystal and appropriately align with our specifications.

The new 53200 Series counters (53210A, 53220A, 53230A) offer an optional battery (Option 300) to enable timebase stability and accuracy. With Battery Option 300 installed and enabled, the 53220A/53230A counter can be operated using battery power for up to three hours. Removing AC power when the battery is enabled switches the counter to battery power automatically with no interruption of operation. Similarly, there is no interruption in the transition back to line power, provided line power is connected before the battery is disabled.

Note: For information on Quartz (Crystal) Oscillators (the type used by the counter's time base), refer to the application note, Fundamentals of Quartz Oscillators, in the "Related Links" below.