Shipped BCM Electronics

Beam current electronics shipped Feb 6^th, 2002.

Gain settings were :

Gain channel 1= -1.19353E-5

Gain channel 2 = -1.1795313E-5

A simple “rough” calibrator for system checkout was added to the back of the PCI board. It was breadboarded in a few days to provide a functional test capability only, not to provide guaranteed calibration accuracy to the specifications of the BCM. A dual monostable multivibrator (74123) was used to develop a calibration pulse. It was adjusted to trigger from the same trigger pulse that starts data acquisition, provides a delay of 1.15ms, and a calibration pulse of 250us. This leaves a quiet time (space) of 100us before the beam burst starts (1.5ms after start pulse).

The pulse is fed through a 1K resistor to a 1N4148 diode to provide a modestly regulated pulse of 530mV to a video amplifier. The amplifier also has a zero offset adjustment potentiometer to zero the amplifier output offset due to digital logic baseline error and amplifier offset. The video amplifier (EL2003C) is isolated from the output coaxial cable by a 50.33 Ohm series resistor, providing source termination. The coax cable return is passed through a 1.0033 Ohm current monitoring shunt (Caddock Electronics, Inc. SR10-1.00-1%) to ground.

The result is a pulse generator producing a 265mV pulse into a 50 Ohm load, and a measured 52 mV out of an un-terminated 20dB pad. The transformer is estimated to provide a 1 Ohm load, therefore, if the 20dB pad feeds the calibration winding, it will provide the equivalent of 10.196 mA (.052*10/51) considering the calibration winding of 10 turns. The channel gains have been adjusted to provide this calibration as documented earlier.

Note: Connecting the calibrator will potentially add noise errors to the data. Furthermore, if transformer windings have a common ground the calibration signal will drive currents into the shield of the signal input cable and can introduce errors (both DC and noise). Additionally, this rough calibrator can exhibit amplitude and offset drift due to power supply changes and temperature. The calibrator is intended as a system checkout aide, and not as a reference device.

Also, recall that the calibration winding on the current transformer requires a 50 Ohm termination at all times for proper transient response of the output winding. Therefore, assure a proper termination for the calibration winding even when the calibrator is disconnected.