9103 Picoammeter bias modes

9103 Picoammeter bias modes

This post explains the 9103 picoammeter bias modes and also explains the concept of “floating”.

There are 4 picoammeter bias modes:

No bias – the current source is connected directly to the picoammeter input

No_bias_functionality

Internal – a low noise DC supply (two 45 V DC batteries in series) provides a bias between the current source and the input of the picoammeter. This application is typically used for providing a +90V bias to a target in a vacuum chamber in order to prevent secondary electrons from leaving the sample. Adding the 90V bias results in a more accurate measurement for both electron and ion current. It is also possible to use regular 9V batteries and so lower internal bias voltages are possible. Batteries are used for the internal bias as they are very clean with no ripple.

Internal_bias_functionality

External – An isolated low noise voltage source (provided be the user) is inserted between the current source and the input of the picoammeter. Isolated means that the voltage source is not referenced to ground. A typical voltage supply has the negative lead referenced to ground internally. If you were to measure the resistance of the supply negative lead to the chassis ground it would have a resistance of less than 1 ohm. On an isolated supply the resistance between the negative lead and the chassis ground would be open.   The maximum voltage that can be applied in this mode is 600V DC (that is the rating of the BNC input on the 9103 USB picoammeter).

External_bias_functionality

Floating – In this mode the picoammeter signal ground is raised from near chassis ground up to a value as high as 1500V DC.   If you were to measure between the signal input and the signal ground reference the voltage would be low (under 1V typically). However measuring the DC voltage from the signal reference to chassis ground the voltage would be high, the floating supply value.

Floating the 9103 Functionality

When floating the 9103 USB picoammeter there are some safety considerations. First of all, the input to the 9103 is changed from a BNC to either a SHV or MHV connector (user specified). These connectors are rated for up to 5kV. The recorder output on the back of the 9103 also floats. For example if you apply a floating voltage of 1000V the recorder output would also measure 1000V with respect to chassis ground. So if you are using the recorder output and also floating the 9103 the meter that you are measuring the recorder output with also needs to be isolated from ground. Finally, to prevent voltage spikes a current limit resistor is placed between the floating supply and the 9103 signal ground.   The floating mode is typically used to measure the collector output of an electron multiplier or a Faraday cup.

The floating mode cannot be used with either the internal or external bias modes.

For all modes of operation the chassis ground of the 9103 USB picoammeter should be connected to the ground on the PC or chamber.

If you would like more detailed information please contact us via email at tech at rbdinstruments.com

9103 Actuel Beta: Data Cursor and Auto-save

UPDATE: A new Actuel Beta featuring a data cursor and auto-save is now available.

Actuel, RBD’s Windows application for controlling the 9103 USB Picoammeter, has currently been updated with some great new features. While the official release is a few weeks away, the beta release contains some new features in addition to the previously previewed micro-window display.

Auto-Save while recording:

In response to customer requests, we’ve added a feature to automatically save data while recording. The auto-save feature comes in handy when leaving the 9103 unattended for long periods. While rare, brownouts, etc., can cause a temporary communication failure between the 9103 and PC, and USB failures can sometimes lock-up or crash a system. Auto-save ensures that data is stored to a text file every 5 minutes, and again when recording is stopped (for completeness).

Auto-save always works automatically when multiple 9103 picoammeters are synced together. Simply select the option for all instances of Actuel, then select the file name (and keep the Data window open for each instance you want to record/save from). The data from each 9103 will be appended to the file sequentially, separated by the device identifier.

9103 Actuel Auto-save Feature

Data Cursor:

Sometimes it’s handy to see the exact data at a particular point in time during or after data acquisition. While high sampling rates make it difficult to mouse-over every data point in large data sets, the data cursor can help track current vs. time more easily without the need to export data as text. By simply hovering over the graph, a vertical line appears, while current and time is displayed in the upper right-hand corner of the graph window.

actuel-data-cursor

As always, Actuel is free for all owners of a 9103 Picoammeter. Meanwhile, you can download the most recent version of Actuel here:

Download Actuel for the 9103 USB Picoammeter

More Information on the 9103 USB Picoammeter

9103 Picoammeter Actuel Update: Micro Window Display

Link

UPDATE: A new Actuel Beta featuring the micro window display is now available.

The Problem: Using Actuel to control and measure current with the 9103 Picoammeter takes up valuable screen real estate:

Actuel is RBD’s Windows application for controlling the 9103 USB Picoammeter. It also provides features like measuring, recording, and graphing current. Although the data recording and graphing display is a separate, optional window, the controller  and measurement window still take up quite a bit of screen real estate.  Sometimes, you just want to display the current unobtrusively while performing other work on your PC.

The Solution: A “Micro” version of the Actuel window that displays only the current and stability.

In response to customer requests, we’ve added a miniature display option to Actuel. By selecting an option in the main window, you can instruct Actuel to display a smaller window when minimized. This windows is much smaller than the main form, yet large enough to be viewed at some distance – a handy feature in many lab environments.

This “micro” window can be moved anywhere on screen and is always displayed on top of other windows. This allows you to use other applications (like RBD’s AugerScan) while simultaneously monitoring current without taking up precious screen real estate. The micro current display window provides a subset of the information available from the 9103 Picoammeter, including the current measurement and polarity, the sampling status, and the range status. There is also an warning overlaid upon the current measurement should the sample be unstable.

If you are using more than one 9103 Picoammeter and running multiple instances of Actuel, you can display a separate window for each 9103. The “micro” window displays the firmware identifier for each individual 9103 picoammeter so you can keep track of which 9103 Picoammeter each display is associated with.

This feature is just one of many additional features coming to Actuel, which will include a data display cursor, and auto-save-to-file while sampling. As always, Actuel is free for all owners of a 9103 Picoammeter! Meanwhile, you can download the most recent version of Actuel here:

Download Actuel for the 9103 USB Picoammeter

More Information on the 9103 USB Picoammeter