PicoQuant GmbH HydraHarp 400 Software V. 3.0.0.1
7. Problems, Tips & Tricks
7.1. PC Performance Issues
The HydraHarp device and its software interface are a complex real–time measurement system demanding
appropriate performance both from the host PC and the operating system. This is why a fairly modern CPU and
sufficient memory are required. The screen resolution should be at least 800x600. At least a 1 GHz processor,
1 GB of memory and a fast hard disk are recommended.
In order to maintain correct interaction between the measurement hardware and the display of histogram
curves and user input, the operating system’s message passing mechanism is used. It is recommended not to
overload the system by running other processes in the background while measuring with the HydraHarp. The
PC’s own occasional network activity should be no problem but running the machine e.g. as a server for other
PCs is not recommended. In principle, of course, any kind of background activity is allowed. Should the system
become overloaded the HydraHarp histograms will not be "wrong" or distorted, but measurement times and
display rates may become irregular. You can even iconize the HydraHarp during measurements without doing
damage. This may be of interest for lengthy measurements in integration mode, where one is only interested in
accumulating a certain amount of counts without need for permanent monitoring. The "panel meters" showing
the current count rates are not meant to be 100 % accurate. They merely serve as an aid for setting up the
system. Some of them may suffer from system overload. Accordingly the values shown in the curve details
(trace mapping dialog) are subject to such tolerances.
In TTTR mode, system overload will manifest itself in loss of data. Here no other background processing
should be allowed. The faster the PC, the less these issues will matter. TTTR mode performance (i.e. max.
throughput without loss) may also be improved by de–fragmenting the hard disk before long measurements.
7.2. USB interface
In order to deliver maximum throughput, the HydraHarp 400 uses (dependent on the model you purchased)
USB 2.0 or USB 3.0 bulk transfers. Correspondingly, the HydraHarp must rely on having a suitable host
interface of appropriate speed rating. USB 2.0 host controllers of modern PCs are usually integrated on the
mainboard. Unless your PC is fairly new, USB 3.0 interfaces may need to be upgraded as PCIe cards.
Throughput is usually limited by the host controller and not by the HydraHarp. Make sure that the host
controller drivers are correctly installed and up to date. This may require using the mainboard manufacturer's
driver disk rather than relying on Windows drivers. Note that some of the early USB 3.0 host controllers still
have immature drivers and possibly flawed firmware. Check the mainboard manufacturer's website for updates
if you encounter problems. For best performance, do not run other bandwidth demanding devices on the same
USB interface when working with the HydraHarp. USB cables must be rated for the intended USB speed. Older
cables do not meed this requirement and can lead to errors and malfunction. Similarly, some PCs have poor
internal USB cabling, so that USB sockets at the front of the PC are often unreliable.
7.3. Histogram Artefacts
Disturbing histogram ripple is strongly dependent on the quality of the input signals. Try to deliver the best
possible signal quality with clean and steep active edges and without overshoot and ringing. It is recommended
to use detector and sync signals of similar amplitude to avoid excess crosstalk. If the PDL 800–B picosecond
diode laser is used, attenuating the sync pulses by 10 dB immediately at the laser driver may reduce histogram
ripple (set CFD level accordingly). Always use good quality 50 Ω components and coax leads with proper
shielding and correct termination. We recommend cables of type RG223 with double braided and silver plated
screen. Check your setup for ground loops. Grounding different system components (PC, detector, detector
power supply, diode laser driver, etc.) at different points can induce considerable noise in the ground lines.
Because signal return paths may share the same ground lines, this noise is copied into the signal lines and
causes increased timing jitter and / or histogram ripple. Network cables and mobile phones may also be
sources of surprising noise. Use properly impedance matched power splitters (reflection–free T–pads) if
signals must be fed to multiple 50 Ω inputs. Never use ordinary Tees. All accessories are available from
PicoQuant. PMT detectors should be connected through a suitable high speed preamplifier (available from
PicoQuant). MCP–PMT detectors should be connected through an amplifier with slightly higher gain (e.g.
PAM 102–M from PicoQuant). TTL–SPAD–detectors (e.g. Excelitas SPCM–AQR) must be connected through a
pulse inverter (PicoQuant SIA 400).
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