Electron microscope sample holder fluid handling with independent pressure and flow control
A fluid metering system for gas independent pressure and flow control through an electron microscope sample holder includes: a pressure control system that supplies gas; an inlet line providing gas from the pressure control system to the sample holder; an outlet line receiving gas from the sample holder; and a variable leak valve that controls gas flow in the outlet line. The gas flows from an upstream tank of the pressure control system through the sample holder and variable leak valve to a downstream tank of the pressure control system due to the pressure difference of the two tanks as the variable leak valve meters flow in the outlet line. Flow rates are established by monitoring pressure changes at source and collection tanks of known volumes with gas independent pressure gauges. A method of directing the gas flow to a residual gas analyzer (RGA) is also presented.
1. A system for controlling fluid flow through an electron microscope sample holder, the system comprising:
a pressure control system that supplies gas;
an inlet line for providing the gas from the pressure control system to the sample holder;
an outlet line for receiving the gas from the sample holder; and
a variable leak valve that meters the gas flow in the outlet line,
wherein the gas flows from an upstream tank of the pressure control system through the sample holder and variable leak valve to a downstream tank of the pressure control system due to a pressure difference between the upstream tank and the downstream tank, and
wherein flow rate is calculated based on a rate of change in pressure in at least one of the upstream and downstream tank.
2. The system of claim 1 , further comprising a boom for supporting the variable leak valve in proximity to the sample holder.
3. The system of claim 1 , further comprising an onboard gate valve at the sample holder.
4. The system of claim 1 , further comprising an inline residual gas analyzer (RGA) between the variable leak valve and pressure control system.
5. The system of claim 4 , wherein the variable leak valve is mounted directly to the RGA.
6. The system of claim 4 , wherein the variable leak valve and the RGA are upstream of the downstream tank.
7. The system of claim 6 , wherein the RGA analyzes composition of gas from the outlet line to characterize reactions in the sample holder.
8. The system of claim 7 , wherein the RGA analyzes gas composition proximal the sample holder.
9. The system of claim 6 , wherein the RGA analyzes composition of gas from the outlet line to characterize reactions in the sample holder and to reduce subsequent reactions or other activity of gas species drifting along the outlet line.
10. The system of claim 6 , wherein the variable leak valve is upstream of the RGA.
11. The system of claim 6 , further comprising a boom for supporting the variable leak valve in proximity to the sample holder.
12. The system of claim 11 , wherein the RGA is upstream of the boom and downstream of the variable leak valve.
13. The system of claim 1 , further comprising a valved residual gas analysis (RGA), wherein a valve selectively directs outlet gas from the outlet line to the pressure control system or RGA.
14. The system of claim 1 , further comprising a direct residual gas analyzer (RGA), wherein the outlet line goes directly to the RGA.
15. The system of claim 1 , wherein pressures in the upstream and downstream tank are measured with gas independent pressure gauges.
16. The system of claim 1 , wherein the upstream tank and the downstream tank each have a fixed volume.
17. The system of claim 1 , wherein flow rate is calculated through software or firmware controls.
18. The system of claim 17 , wherein the variable leak valve is adjusted through software or firmware controls to achieve a target flow rate.
19. The system of claim 1 , wherein a largest pressure drop in the system is across the variable leak valve.