1. ULTRA LOW CURRENT MEASUREMENT SYSTEM

2. A full diagram of a mass spectrometer

3. Ionisation

4. Block diagram SOURCE OF CURRENT (pA-µA) I-V CONVERTER (LMC6001) ADC (CS5531) MICRO CONTROLLER (P89C51) COMPUTER

5. ADC Software CS The CS pin is tied low, the port can function as a three wire interface. SDI Serial Data In, The data signal used to transfer data to the converters. SDO Serial Data Out It is used to transfer output data from the converters. The SDO output will be held at high impedance any time CS is a logic 1. SCLK Serial Clock It is used to control the shifting of data to or from the ADC’s serial port. The CS pin must be held low (logic 0) before SCLK transitions can can be recognized by the port logic.

6. Timing Diagram