Operator Safety:

An operator servicing a 1440 system may require a PANIC OFF capability when working some distance from the 1440 main frame. The "Interlock" on the front of the 1441 is for this purpose. A ground or 50 ohm terminator connected to this BNC will cause a PANIC OFF and disable the 1440 system.

1443 Voltage and Current Control Limits:

The 1443 was designed for use with PMTs so it has only two sets of voltage and current limits (one set for 1443N and one set for 1443P) that apply to all 1443 channels in one main frame. These limits apply ONLY to 1443 modules and not to 1444 modules if they also are in the same main frame.

• The voltage limits (one negative and one positive) are manually set by locking potentiometers on the front panel of the main frame (front panel of 1441). These are analog limits that clamp the feedback of a channel's HV dc-to-dc converter if it exceeds the set limit. The safest way to set these limits is with the HV on and one channel set to the voltage at which the limit is desired. Adjust the limit potentiometer until the output voltage of that channel starts to drop. Lock the potentiometer in place. Because this is an analog control, expect variations from channel to channel.
• The current limits (one negative and one positive) are digital values loaded by software and therefore are not quite so robust as the volt limits. Each HV channel has its dc-to-dc converter ground isolated from the chassis ground by a resistor whose voltage is proportional to the current output of that channel. This voltage is used to clamp the dc-to-dc converter feedback if the output current exceeds a preset value which is the programmed current limit. The safest way to set this value is to monitor the output voltage of all channels when fully loaded and adjust the current limit to slightly greater than what effects the output voltage. Again, this is an analog control so expect variations from channel to channel.

The 1444 was designed for wire chambers so there are a number of limits and/or trips. All limits/trips apply ONLY to individual 1444 cards and NOT to the main frame. All limits/trips are analog and therefore will vary from channel to channel.

• A hardware voltage limit is provided for each channel. Potentiometers on the front panel of the 1444 allow setting a limit on the programmed voltage to each dc-to-dc converter. The safest way to set this is to monitor the channel while programmed to the desired limit voltage and adjust the potentiometer to cause the observed voltage to start changing.
• All other limits (AC and DC current) are Trips where if the software set limit is reached, a flip-flop is clocked and the channel is ramped down along with any other interconnected channels. The setting and controlling of these limits requires more detail than is allowed here so the user is referred to the 1444 manual. Please note that the AC trip can be effective. A 1444 user was having trouble with one HV channel always tripping but when another type HV supply was used, the chamber operated with no problems. He left it on the other supply and after some interval a wire that was powered by that supply broke.