Calibration signals are generated using pulse generators powered by a variable voltage power supply. With reference for Fig.1, a 100-bit shift register contains a stage for each PS straight section. Forty pulse generators are connected to taps 0, 3, 5, 7, etc., i.e., to each tap corresponding to a straight section with a position pick-up. The shift register is continously clocked at 31.25 MHz. When Cal-En is asserted, a single '1' bit is inserted at tap 43. This '1' is kept circulating in the shift register for as long as Cal-En remains set. Each pulse generator produces an output pulse as the '1' bit sweeps by, thus simulating a single-bunch beam circulating in the machine at f_rev=312.5 kHz.

The pulse generators are powered by a variable voltage power supply. This allows the intensity of the simulated beam to be set. The power supply is controlled from a VMOD-12A2 DAC, set to put out 0-10V for its 0..4095 range. The power supply is a Glassman 150-7, which has a voltage transfer gain of 32 and a full-scale at 5V. The wiring between the DAC and the power supply is detailed in Fig.2. With the resistor divider in Fig.2, that yields V_out=0.0244 N.

The power supply doesn't drop very fast. When the system has been used to calibrate a high intensity setting, it may take several cycles before it drops back down to levels compatible with low-intensity settings. To help it along, a 100 mA Constant-Current load has been connected to its output (Fig.3). This load will go into auto-protect shutdown for voltages above 50 V though, so it will act only below that level. (Which is also where the fall is slowest, so that's OK.)

Fig.3: Constant-Current load