New high speed 5kV floating Picoammeter

RBD Instruments has released a new version of its 9103 USB Picoammeter which incorporates faster reads per second with 5000 DC volts of isolation to chassis ground.

9103 HV

9103 HV

 

 

 

 

 

 

 

 

Increasing the DC voltage isolation from chassis ground to 5000 volts (5kV) opens up new possibilities for researchers such as direct DC current measurement of very small electron and photo multiplier signals.  Electron and ion beam measurements can be biased to reduce secondary electrons or to retard the beam as needed for experiments.

Designed to provide accurate bipolar DC current measurements in noisy environments such as synchrotron beam lines, the 9103 can measure bi-polar DC currents from low picoamps to milliamps.

The drawing below shows how the 9103 is floated on your HV power supply.  The high voltage is referenced to chassis ground, and the signal ground is referenced to the high voltage.   To help keep the supply and signal connections clear, the HV connection is a MHV connector and the signal input is a SHV connector.

Floating picoammeter

Floating picoammeter

 

There are a number of manufacturers of programmable DC power supplies that can be used to float the 9103 up to whatever voltage is needed (as long as you do not exceed +/- 5 kV).

For example, TDK-Lambda provides a programmable 0 to 6.5kV supply that can be voltage limited to 5 kV and can drive up to 2 mA of current.

The model number for a 120 VAC line input is PHV6.5P2-USB-1P115.  The base model has a ripple of 700mV which is somewhat high, but TDK-Lambda does offer a low ripple option that gets the ripple down to 75mV.  You can also easily make a simple RC filter to do the same thing.    A number of interface options are available (USB, Ethernet, Serial, analog….

TDK Lambda supply

TDK Lambda supply

 

 

 

 

PHV series

PHV series

 

 

 

 

 

 

 

 

The new high speed option for the 9103 increases the reads per second from 40 to over 500, which is fast enough to perform optical chopper experiments.  And, by taking more reads in the same amount of time as the first generation 9103 could, the accuracy is improved.

The Actuel software included with the 9103 provides new features for high speed acquisitions and display, but you can also write your own software to control the 9103 using the simple ASCII commands or in LabVIEW.

Since 9103s can be synced, it is now possible to configure a multichannel DC Picoammeter with up to 256 channels that has high speed, high voltage, or both options.

And if you do not need the high speed or high voltage options, the standard 9103 USB Picoammeter is still available as well.

For more information visit the RBD Instruments website at http://www.rbdinstruments.com

 

How to test the bias batteries in a 9103 picoammeter

The 9103 USB picoammeter is often equipped with a +90 V bias option which improves the accuracy of electron and ion current measurements (by reducing the number of low energy secondary electrons that are generated by the beam from leaving the target).

The +90 V bias comprises two 45V batteries in series which are located inside the 9103 chassis.   This blog post will explain how to test and replace the batteries in a 9103 picoammeter.

1. Connect a DVM (digital volt meter) to the 9103 Input BNC connector.  A BNC to double banana cable works well.  Set the DVM to DC volts.

2. In Actuel (the 9103 software), select the input Grounded and bias On.

3. Sample the current.

4. When the bias ON is checked there will be about +90V DC on the input of the 9103.

5 .The input impedance of most DVMs when measuring DC voltage is 10 meg ohms.  The two 45 volt batteries should total 90 to 95V DC.    The bias voltage divided by the input impedance of the DVM will  equal the current.  In this case the voltage of the two 45 volt batteries totaled 94V and the current was 9.414 uA.

9.4 uA in Actuel

9.4 uA in Actuel

 

 

 

 

 

 

 

94 V DC on DVM

94 V DC on DVM

 

 

 

 

 

 

 

6. It is recommended that the bias batteries be tested every 6 months and replaced when the voltage drops below 80 volts.  It is normal for the batteries to wear out over time and with use.  Once the bias voltage drops to less than 50 V the effectiveness of preventing secondary electron emission is greatly reduced, which in turn reduces the accuracy of electron and ion beam current measurements.

The RBD part number for the 45 V battery is BAT-45-213.

Whether you have an RBD 9103 USB picoammeter or an older Keithley with a PHI model 78 bias box, you should test the batteries as part of your preventive maintenance procedure and replace them as needed.

To replace the batteries in a 9103:

Unplug the 9103 USB power and input cables.

Using the Torx wrench that was included with the 9103, remove the screws from the front and rear 9103 chassis covers.

Slide the board out from the front of the 9103.   You will need to rotate the back cover to feed it in. The back cover has a ground wire that is attached to the 9103 board. Also note which groove the 9103 board is in as you will need to put it back in the same groove.

Remove the battery support bracket (white plastic).

Carefully remove the old batteries.

Install the new batteries.You may need to adjust the contacts on the batteries to get them to fit onto the board snaps more easily.

Reattach the battery support bracket.

Carefully slide the back cover and board back into the chassis. Make sure that you put the board back in the same groove that it came out of.  If the front cover does not line up with the chassis then you are not in the correct groove.

Reattach the screws to the front and back covers.  Do not over tighten the screws!

Once you have installed the new batteries, test the voltage. You should have 90 to 95 Volts.

9103 bias batteries

9103 bias batteries

 

 

New Feature: Use the 9103 Picoammeter to Automatically Read microCMA Target Current

The latest software releases of Actuel for the 9103 Picoammeter and CMapp for the microCMA now support the ability to automatically read target current when acquiring data.

To use this feature, you must (of course) have a 9103 Picoammeter running RBD’s Actuel software.

Run CMapp for the microCMA, select Hardware Properties from the System menu, and check the option “Use 9103 Picoammeter to read target current.” You only have to do this once.

Turn on the 9103 Picoammeter, run Actuel, and measure your target current as usual. Leave Actuel open. It doesn’t matter whether the 9103 is sampling, but keep in mind that your current settings (sample rate, etc.), will be used.

Now, whenever you take an acquisition (except for an alignment), the target current will be measured at the beginning of the acquisition and displayed with the other electron gun settings when the acquisition is complete.

If you don’t have a 9103, you can still manually enter a value for the target current in the acquisition dialog.

Download the latest release of Actuel for the 9103 Picoammeter here.

Download the latest release of CMapp for the microCMA here.