RFD VS picture


Operation of the Fermi RFD-VS

Each scaler can be operated in anyone of three modes; individually, bussed and manual or pre-scale (predet) (ratio).

The individual mode allows each scaler to be operated independantly; L (Local).

The bussed mode allows any one scaler to be the master and either or both of the remaining to have the gate and reset signals slaved to them. The master scaler MUST select B (BUSS mode). This internal buss routes the gate and reset signals to the scalers that have the front panel switch set to B (Internal BUSS).

The manual mode is the one in which the signals from the front mounted gate and reset switches can be selected and used by any or all of the scalers; M (Manual). The reset switch does not reset the gate. The gate switch toggles the gate flip flop.

In the prescale (predet) mode, the right most scaler acts as a "pre-det" for the other two if they select the M buss. The rotary switch between the middle and the right most scaler selectes the power of ten that will reset the gate. With the switch in its most counter clockwise position this mode is disabled. The reset (NIM) signal is placed on a lemo fitting on the rear of the unit. When using this mode at high rates, you will see a small overcount. This is due to delays in the reset path for the gate and efforts are under way to reduce this. However it is a small effect and shouldn't interfere with the evaluation of the unit.

All inputs to the unit are NIM level. The reference point is ~-.35 volts. The signal input is terminated by a 50 ohm resistor. The two pairs of gate and reset inputs are jumped together internally; each pair terminated by a 10K ohm resistor. This allows one source to be chained to many units. Of course the last unit should have a 50 ohm terminator plugged in to eliminate reflections.


The units will count pulse pairs consisting of two 5 ns pulses whose leading edges are separated by 10 ns. At a continuous rate, it will toggle at over 90 MHz.

The unit runs fairly cool and should require no special treatment in this regard.

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