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Analyte 2000
Frequently Asked Questions
About signal handling in the Analyte 2000.
The analog signals are first converted to a voltage in a current-to-voltage amplifier. Further gain stages increase the signal level. Relays are used to control the overall gain level. A synchronous detection method is used to subtract out stray background light.
Why does a measurement result become 1/2 of a true signal value?
This is a matter of choice and has no impact on resolution. Since the excitation duty cycle is 50%, the average signal is half the peak signal. The signal could also be given as the peak value.
When the output from PD was 10pA, the result becomes 5pA.
See above.
What kind of method does Analyte 2000 do calibration by?
We inject a slowly increasing current into the current-to-voltage amplifier IC and monitor the output voltage at the different gain transitions. This current is created by a D/A voltage being applied to a high value resistor. Correction factors are then applied to each gain level to obtain seamless transitions. The correction factors are stored in nonvolatile memory.
What do you use a temperature sensor in the circuit for?
This was included in case it was necessary to compensate in software for temperature sensitivity of gain resistors and other components. It is only monitored at present, and is not actually used in any calculations.
The reason that another optical fiber is connected between LD - optical connectors?
We did not directly inject light into the Analyte's external cable because we wanted a modular design where users could buy from one to four channels and all electro-optics for a single channel would be on a single card. They could then buy extra cards at a later time and install them with less risk; this also allowed us to place the light source away from the exterior. Exterior mounting may make the laser diode and beam-projecting optics more subject to external temperature changes, physical damage, mechanical shock, water spills, and EMI. There is very little space in the Analyte box and by using a fiber with a thinner protection jacket inside the instrument, it was not difficult to route the laser light to the exterior of the box. We did not hard-wire the fiber to the laser block because if a user breaks an external fiber cable, it is then not necessary to open the instrument for repair. We have found a higher rate of laser diode failure when the instrument is opened, even if the technician takes care to be grounded. It is advantageous to use a slightly larger fiber within the instrument so that alignment of the fiber with the laser diode is eased, and minor changes in alignment over time do not cause the excitation power delivered to the exterior to change.
A choice standard of length of the optical fiber?
There is no optimum length. A very long fiber cable will typically be less affected by cable bending due to the loss of leaky modes in the longer cable.
