LabSmith: High Voltage Sequencing FAQ

The following are answers to frequently asked questions regarding LabSmith High Voltage Sequencers.

Which cables should I use with my HVS?

We recommend LabSmith HVC High Voltage cables whenever using an HVS sequencer. The cables in our standard cable sets each include a 10k-Ohm resistor to protect the HVS circuits from accidental overloads and shorts. This will cause a small voltage drop across the cables (ranging from up to 120V for the HVS448-1500 to 30V for the HVS448-6000D). For applications in which this voltage drop cannot be tolerated we recommend the HVC High Current cables, which do not include the current limiting resistor. Either type of cable set is available in Standard or Long lengths. You can also add Micro clips for easier positioning (WARNING: clips are not voltage rated and should never be touched while voltage is present. See Safety Sheet for more).

Can the HVS create sinusoidal voltage or other waveforms?

Yes. Software wizards included with the HVS make it easy to to generate waveforms such as sine, ramp, sawtooth, and square waves. Each channel can produce a different waveform, and all can be synchronized. For example, several channels could be programmed to produce sine waves with different amplitudes and a fixed phase difference, different frequencies, etc.

How fast can I switch between potentials?

Running an internal sequence, the HVS can change the function of each channel between voltage- or current-regulated output or high impedance input at 0.1 ms intervals (10 kHz). Controlled via the computer interface, the rate of output switches is limited by the bus speed: you can switch the function of a single channel at about 500 Hz; you can switch multiple channels simultaneously at about 100 Hz. With voltage-regulated outputs, the voltage rise and fall time is typically 0.5 ms, depending on the load. Current regulation is about 10-30x slower.

Can I set the outputs independently?

Each channel can be set to an arbitrary voltage within the selected voltage range, so yes, you can have all channels at different voltages. You can even have some channels regulating voltages, others regulating currents, and others functioning as inputs. The channels can switch voltages or modes from inputs to outputs at the same time or at different times. The only limitations are: the total current from all channels cannot exceed the spec, and the voltages cannot exceed the selected voltage range (e.g., 0 to 3000 V).

When a channel is not active, is the connection left open or held at ground?

When a channel is not active (when it is an input) it looks like a precision 200 MΩ resistor to the chassis ground.

Can I force ground to be a negative potential?

The HVS448 chassis, which is exposed metal, is tied directly to ground. The case must for safety reasons be tied directly to a good earth ground. You can simply set one of the 8 output channels to a negative voltage, if you need a common negative voltage (negative ground).

Can you explain "output voltage" and "max voltage differential"?

Any channel of an HVS can source up to the maximum output voltage listed in the HVS product table. For example, any channel of the 6000D can source from -3000V to +3000V, relative to the chassis ground. The max voltage differential is the maximum voltage between two channels. With the 6000D the max voltage differential is 6000V, when one channel is set to -3000V and one is set to +3000V.

What is the difference between the HVS3000 and HVS3000D?

Both the HVS3000 and HVS3000D can provide 3000V maximum voltage differential between channels. In the HVS3000 the output voltage range is switchable, such that all channels can source -3000V to 0V, -1500V to 1500V, or 0V - +3000V. The channels of the HVS3000D can source voltage within the range of -1500V to +1500V only.

When you connect conventional high voltage supplies to a microchannel, the lower voltage output floats higher. Does this happen with the HVS448?

No. The channels are fully regulated and will sink and source current as needed to hold the voltage. This is critical when the channels are used together in a network like most microfluidics applications.

Can each channel hold a different potential and well as polarity independent of the others?

The -3000V model has three switchable output voltage ranges: 0 to 3000 V, -1500 V to 1500 V, and -3000 V to 3000 V. Each channel can regulate independently to any voltage in the output voltage range (and can switch between voltages as well). You cannot set one channel to -3000 V and another channel to 3000 V at the same time (a common question).

Is it possible to change voltage on one or more channels in mid-sequence while operating by LabView commands?

You can send manual commands at any time (e.g., via LabView) and they will work normally, but they can be superceded by the sequencer if the program is written this way.

Can your HVS448 run several voltages and currents on each of the eight channels? We need to first run 1500-3000V and a few uA, then continue at 200-400V but several mA.

The 3000V unit can supply and sink somewhat more than 6 mA at any voltage in its output range, so it should be able to handle this application. It is not architected to be able to supply more current at lower voltages. We do have models that can supply more current (e.g., the -800V, -400V) over a reduced voltage range.

What is the output noise level?

There is a 300 mV noise floor when passively regulating the output voltage (digital fine-tuning off), predominantly in the kHz range over most of the output range, excluding very low voltages (<100 V). The digital fine-tuning typically doubles the noise level, predominantly in the 100 Hz range, but improves absolute accuracy.

The tolerance for voltage seems high when we program in voltages under 100V.

The HVS is designed for stable and agile function at higher voltages. Unfortunately, this means the performance at lower voltages and output currents can be noisy. There are some simple tricks to resolve this problem: if you want to supply a potential difference of 100 V across a device, you can connect it to two outputs and apply a higher common-mode voltage to operate in the low-noise range, e.g., apply 500 V to A and apply 400 V to B for a 100 V differential. If you must operate below 100 V referenced to the case ground, you can stabilize the output by loading the channel with an external resistor either to ground or preferably to a voltage applied by another channel so that several 10s of microamps flow from the channel. Make sure the resistor can take the applied power and that the resistor does not overload the channel.

Do you have any instructions for working with the HVS488-3000 driver posted on your website?

Several complete examples are included in the library (*.llb). In LabView, open the library (e.g., HVS3000V.llb) for browsing. You will see a number of virtual instruments (VIs) you can use, but there are a few tricks to using them correctly. First, review SetAllVoltagesAndSample.vi or SetVoltageAndSample.vi to see how these common actions are done. You must first run OpenHVS and pass its output to subsequent command VI’s. When you are done communicating with the HVS, run CloseHVS to release the serial port. By reviewing the sub-VI’s you can directly observe the functions of command forming, response parsing, etc.

Tip: The VI’s are distinguished by colored icons in the library. Typically you will only use VI’s having green icons. You might occasionally use or adapt VI’s having yellow icons, but you will probably not directly use VI’s having red icons---these are lower level routines.