1. 问：How to set the energy of DPR300

答：Hi Eric,

The simplest explanation is to view the front-control panel of the DPR300 from our website or the User’s Manual. The website show’s this image in a large JPEG image which you can get if you click on the same smaller image on the DPR300 product page.

http://www.jsrultrasonics.com/images/dpr300b.jpg

You can see that there are 4 Energy Selections that are independent of the 2 Impedance Selections (High, Low) so that the single control-knob (for the front-panel control versions of the DPR300) has a total of 8 selections. You get those same selection options when using the computer-controlled instrument using our JSR Control Panel Windows software that is supplied with any DPR300 that has the computer-controlled serial port interface.

Electrically, the Impedance Selection is a series resistance between the pulser output and the T/R connector going to your transducer. You can select Low Impedance (maximum energy transfer rate to your transducer) or High Impedance (slower energy transfer rate to your transducer) with the High Impedance effectively extending the pulse-width of the negative-spike pulser output. The actual effect will of course vary with the capacitance and the impedance of your transducer. This series resistance is of course not in the receiver path for the return echoes from your transducer, only in the pulser output path.

The Energy Selection does change the total energy supplied by the pulser when using either of the series impedance options (High or Low). The Energy Selection is also independent of the High Voltage supply level (100V to 475V standard option) that you choose to apply but of course the actual energy achieved in Micro Joules does vary as you change the High Voltage level of the pulser supply. You just have 4 energy levels to choose at each High Voltage Supply level.

In contrast to the Impedance selection options (series resistance) of the pulser, the Damping Settings are parallel resistance with the T/R connector and have the traditional damping effects from changing the damping resistance. The Damping Settings are effectively an additional parallel “load” on the pulser output in addition to your transducer. Our DPR300 is our only pulser-receiver model that has a controllable series resistance and is an added control that is not generally available in other manufacturer’s pulser-receivers. Our DPR500 and other models do not have that series impedance control.

Please let us know if you have any further questions.

Best Regards,

Bob Hibbard

Imaginant Inc.

2. About DPR300 damping resistors.

问：

I have a question that why use too many damping resistors. but NO 50 Ohm. Our BNC cable is always 50 Ohm. 16 Damping values: 331, 198, 142,110, 92, 77, 67, 59, 52, 47, 43, 39, 37, 34, 32, and 30 Ohms. What's the application scenario of these resistance.

By the way, what's the bandwidth of the transmitter pulse.

I find that the waveform are different when change the damping resistors and always with a 50 Ohm end.

答：

Hi Eric,

Sorry for the long delay in getting you some technical answers. Here is some information and if you need additional details, please let us know.

DPR300 Damping Resistor Selection:

In our earlier communication I described the “series damping” unique to the DPR300 and the “parallel damping” that has the selection values that you mention. The parallel damping impedances are the normal control used in almost all pulser-receivers. Those values do not “terminate” your 50 ohm cable impedance. You are correct that the DPR300 is designed to work in 50 ohm cable applications. While there will be some change to your output pulse and the received signals, that is not primarily due to changes in the termination impedance caused by different “Damping Impedance”. Those impedances are primarily only applied when the pulser is firing (the large negative-spike output to excite your transducer). After a small delay, the impedance will be primarily determined by the receiver, which is configured to receive return signals (ultrasound echoes) from the 50 ohm cable and to receive them properly.

That said, the various Damping Impedance values will change the output pulse characteristics, which will change the transducer excitation, which will change the received return signals. That adjustment is intentional and allows you to “adjust” the pulser so that it matches the characteristics needed by the transducer that you are using.

Bandwidth of Transmitted Pulse:

There are two ways to consider the “bandwidth”. One is the total spectrum (like FFT) of the complete excitation pulse (negative spike output) going to the transducer. That sometimes does matter but overall is not the most important characteristic in adjusting the pulser (Damping Values, High Voltage Supply level, Series Impedance for example).

The other “bandwidth” is that of the falling-edge of the negative-spike pulser. That is the primary output that causes your transducer to “react” and output its characteristic pulse which is unique to that transducer model. That will also vary between different transducers of the same model from the same manufacturer. That falling-edge will have a “spectrum” (or bandwidth) that is high enough to initiate a transducer at the maximum frequency specified (really by design) for that pulser-receiver. High frequency transducers will required a very fast falling edge, smaller peak-voltage changes (reduced High Voltage Supply to not over-drive sensitive, high-frequency transducers) and less overall energy supplied. Lower frequency transducers will ignore (cannot respond to…) high frequency content in the falling edge, so the fall-time can be slow with less high-frequency content. However the magnitude may need to be larger (increased High Voltage Supply for higher energy and stronger excitation to a slower response transducer) and while adjusting characteristics, the pulse-width will get longer. This also correlates to the frequency of the transducer you are using because a fast, short pulse to a low-frequency transducer will not excite the transducer long enough to get much response from the transducer. A long pulse-width to a high-frequency transducer may over-drive that transducer and therefore not create the optimum response characteristic of that transducer design.

Receiver Bandwidth:

A separate bandwidth is that of the receiver. That bandwidth will not change as you modify the pulser characteristics. However, as mentioned above, the pulser characteristics will change to allow you to adapt it to your transducer & application. These changes cause the pulse to change shape and will therefore change the return echoes from your transducer because the ultrasound output of your transducer will change somewhat with the Damping Values as well. All of this is “tuning” or “matching” the pulser to your transducer characteristics.

Let us know if you have any further questions. I hope this helps. We can discuss some specific examples with the DPR300 if you still have some questions about the performance.

Best Regards,

Bob Hibbard

以上信息是脉冲发生接收器DPR300的，6006PR也一样的道理。供大家参考。祝大家工作顺利。