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BaBar Drift Chamber

gas System

  Technical documentation for the electronic scales

(updated Sept 17th 2003)

This page lists some technical facts about the electronic scales.

Algorithm to get the right weight after one or several power cut:

The electronic scales, after a power cut, reset themselves to 0, whatever is the load on them. So after a power cut, the weight given by the scales is 0 lb and then will decrease and become negative as the bottles get empty. To get the normal reading, an operator has to come and lift the bottle, reset the scale, put again the bottle on the scale, which is a difficult task given the weight of the bottles!
To get rid of that, an algorithm was implemented in the EPICS software. The idea is to add an offset to the raw value of the weight.

Here is the description of the algorithm:
  - if the raw weight is lower than 10 lb and the previous offset is equal to 0 => offset = previous value of the weight.
(this situation is for a first power cut)
  - if the raw weight is greater than the previous raw weight and the previous offset is different to 0 => offset = previous value of the computed weight (raw weight + offset)
(this situation is in the case of power cut n, n > 1)
  - if the raw weight is greater than 10 lb and the offset is different to 0 => offset = 0
(this situation arises when the scale was reset by an operator)

Settings of the electronic scales:

These settings are very important in order that the electronic scale works. See scale manual p66+ to see how to configure the scale. The setting MUST be as:
  - 1.7.5 (pounds)
RS-232 communication:
  - 5.1.7 (9600 Baud)
  - 5.2.4 (even parity)
  - 5.4.2 (handshake mode: hardware, one char. after CTS)
  - 6.1.2 (print mode: manual after stability)
  - 7.1.1 (printout format: no data ID code)

Setting of the station number:

The station numbers are hardcoded in the GMB module. They are currently 4 and 6. They can be changed if needed (in this case, the EPICS code should be then slightly modified!).
Here are the instruction of Jong Yi to change the station number:

To set the station ID using canProbe*.dl:

- write to address 0x0101 (via command "5") the new station number. This is done by (say you're changing from station 6 to 8):

1. command to be sent is 0x65 via "DATA"
2. bytes to be sent is 4
3. type in the bytes field (0x01, 0x01, 0x01, 0x08) first 2 bytes are the address. Next 0x01 is the number of bytes to write; and the next is the station number
4. reset the GMB card

Notice that number 5, 7 and 15 are not allowed.

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