X-Git-Url: https://git.ucc.asn.au/?p=matches%2Fhonours.git;a=blobdiff_plain;f=thesis%2Fappendices%2Felectron_gun_circuit.tex~;h=c640556391aa5019ccb46ab5d039c591509a9aa9;hp=399270c5fe045918f9550e78cac11f87151b3e3e;hb=ddcdd43bf4077f35beefc59eb8568e13b6c5b3cd;hpb=1c9618e52bd8dad6a84c698967800beee8378f24

diff --git a/thesis/appendices/electron_gun_circuit.tex~ b/thesis/appendices/electron_gun_circuit.tex~
index 399270c5..c6405563 100644
--- a/thesis/appendices/electron_gun_circuit.tex~
+++ b/thesis/appendices/electron_gun_circuit.tex~
@@ -1,5 +1,7 @@
 
-\chapter*{Appendix - Electron Gun Control Circuit}
+\section{Electron Gun Control Circuit}
+
+\subsection{Control Circuit}
 
 The control circuit diagram for the electron gun is shown in Figure \ref{electron_gun.pdf}. The wiring of the circuit, including resistors and potentiometers, was incoroprated into a single box, with external connections available for the power supplies, ammeters, electron gun, and sample holder. Both the components and operation of this circuit are straightforward; we will give a brief overview here for completeness.
 
@@ -40,8 +42,18 @@ The control circuit diagram for the electron gun is shown in Figure \ref{electro
 \end{itemize}
 \begin{landscape}
 \begin{center}
-	\includegraphics[scale=0.80]{figures/egun/electron_gun.pdf}
+	\includegraphics[scale=0.75]{figures/egun/electron_gun.pdf}
 	\captionof{figure}{Circuit Diagram for Electron Gun Control}
 	\label{electron_gun.pdf}
 \end{center}
+
 \end{landscape}
+
+\section{The Ammeters}
+
+An ideal ammeter has no input resistance. In reality, it is not the current that is measured, but the voltage accross a fixed input resistor. This voltage can either be amplified, or the resistance increased, for measuring a smaller current.
+
+Since there is a voltage drop across the ammeter, the potential of the surface relative to the cathode is actually $U + I R$, where $R$ is the input resistance of the ammeter.
+
+The 602 and 610B electrometers both provide a large range of scales and amplifier settings for current measurement. Using a low scale setting increases the input impedance, which increases the potential drop accross the ammeter. However, using a large amplifier gain increases noise; hence there is a trade off. For the 602 and 610B electrometers, a significant drift (typical +5\% of scale in 10min) in the zero level was also observed at high amplifier gains, whilst low gains appeared more stable (+10\% noted after 2 days).
+