9103 USB Picoammeter Filter Settings – Part 1

The 9103 Picoammeter uses a continuously sampling A/D when measuring current. These samples are then averaged using an low-pass infinite impulse response (IIR) filter.

Filter Settings

When using the 9103 to sample current, you have control over the filter response and the degree of smoothing (both in Actuel in when programming the unit). The filter setting will make little difference for most constant signals, but for dynamic and periodic signals, the filter can be set to attenuate noise, or to provide detail and catch peaks.

A filter coefficient that is user-programmable determines the amount of smoothing the filter will apply. The higher the value, the more smoothing of the signal.

The filter can be set to 0, 2, 4, 8, 16, 32, and 64. A value of 0 is essentially the same as bypassing the filter. A value of 64 is the greatest amount of filtering. For most cases, values of 4, 8, and 16 will work best. Higher values may produce more accurate results for stable signals, but it will take longer for measurements to stabilize.

Example

In the examples below, a 1 Hz sine wave is sampled at a 25 mS rate, yielding 40 discrete data points per cycle. Each data point is comprised of multiple filtered A/D readings.

The filter settings used in the examples are 2, 4, 8, 16, and 32.

filter setting 2
Filter Setting 2
filter setting 4
Filter Setting 4
filter setting 8
Filter Setting 8
filter setting 16
Filter Setting 16
filter setting 32
Filter Setting 32

There’s quite a bit of noise present when using low filter values of 2 and 4, while values of 16 and 32 reduce the noise but also attenuate the signal somewhat. For this application, a value of 8 produces the most accurate result.

Conclusion

In general, any low-pass filter will of course mask high-frequency data. While the 9103 is not typically used to measure periodic signals, the filter’s effect on your application may be significant. When in doubt, start with the filter set to 8 for some noise reduction without significant smoothing or signal attenuation.

In Part 2 we’ll discuss use of the additional first-level filter implemented in the high-speed model of the 9103.

9103 USB Picoammeter Winter 2020 News

Last year, RBD introduced an updated 9103 USB Picoammeter, with 3 new models:

  • High-speed: 500 reads / second compared to 40 for the Standard Model
  • High-voltage: an isolated signal input with the ability to float the 9103 Picoammeter to ±5000 VDC.
  • High-speed / High Voltage: One model combining both features.

This year we’ll be working on adding new features to our Actuel application software and providing more comprehensive support and programming documentation.

Actuel 1.6 is Released

Actuel Version 1.6
Actuel Version 1.6


The latest version of Actuel (1.6) is now available, as is an updated User Guide. The guide has new information on setting up and programming the 9103 for high-speed communications. Both can be found here.

This release replaces the Beta release and has full support for high-speed sampling and data recording and graphing.

9103 TechSpot Article Series

This year, we’ll be running a series of articles here on the TechSpot blog with more information on the new 9103 models and features, as well as detailed configuration, application, and programming advice.

Some of the topics we’ll be covering include:

  • Programming the 9103 for high-speed data collection
  • Using the high-voltage reference
  • Proper use of the input ground
  • Troubleshooting 9103 communications

Keep your eye on here on TechSpot for these and other articles covering all of RBD’s products, and please consider subscribing.

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