Leginon

h1. Faraday Cup Measurment Notes

Picoammeter setup:

* plug in

* wait 1 hour

* activate ZCHK (maybe already when turned on) (should say ZC on screen)

* plug into faraday holder

* set to lowest range (2nA)

* activate ZCOR to set zero  (should say ZZ on screen)

* set auto range if desired

* deactivate ZCHK to begin measuring

* focus beam to a spot

* pull out holder until spot hits the faraday cup (max current) (This is a negative value)

Examples

** 200keV

*** 1.21 nA

** 120 keV

*** 2.53 nA

h1. Exposure Time to Screen Current measurment

* refer to Tecnai Help for "Exposure Time, Plate Camera CP"

* formula:  beam current (nA) = 2.15 * emulsion / measured_exposure_time

** exp time is between 3.1 and 3.5 depending on size of beam

** emulsion = 1

** beam current is between 0.61 and 0.69 nA

h1. Leginon screen scale factor measurement

* adjust scale factor until beam current is same as faraday cup

** 200 keV

*** 0.725

** 120 keV

h1. Camera sensitivity

** 200 keV

*** 45-50 count/e

** 120 keV

*** 107 count/e

h1. 2011-02-02 calibration on Tecnai 2:

* faraday measurement:  1.52 nA

* Tecnai main screen measurement (emulsion = 1):  2.15 / 2.6 = 0.83 nA

* Leginon scale factor to match faraday current:  0.793

* Legion measures Tietz sensitivity:  68.7 counts/e-

h1.  2013-02-28  Calibration on T12 Spirit

*  120kV, Filament Heat= 29, step 1, Spot 3, mag 46K, Beam Current = 5.5-7.5 µA, LaB6 installed 2013-02-22

*  TVIPS F416 camera

*  Technai main screen measurement (emulsion = 1): 2.15 / 0.11 = 19.54 nA

*  Leginon scale factor to match Faraday current:  0.991  (was 0.80)

*  Leginon measure Tietz sensitivity: 38.8294  counts/e- (was 32.5211)

h1. Finding the Faraday Cup

* See picture below 

* Center to cup is 4mm

* Use a 6mm or 7mm Allen (hex) wrench as a wedge (spacer) between the holder end cap and stage.  Use the wrench as a lever to fine tune the position