* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download University of LeicesterPLUMERef: PLM-PAY-LabElecsGain-014
Variable-frequency drive wikipedia , lookup
Electrical ballast wikipedia , lookup
Signal-flow graph wikipedia , lookup
Power inverter wikipedia , lookup
Public address system wikipedia , lookup
Three-phase electric power wikipedia , lookup
History of electric power transmission wikipedia , lookup
Audio power wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Electrical substation wikipedia , lookup
Current source wikipedia , lookup
Negative feedback wikipedia , lookup
Dynamic range compression wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Power MOSFET wikipedia , lookup
Oscilloscope types wikipedia , lookup
Power electronics wikipedia , lookup
Schmitt trigger wikipedia , lookup
Alternating current wikipedia , lookup
Buck converter wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Oscilloscope history wikipedia , lookup
Surge protector wikipedia , lookup
Voltage regulator wikipedia , lookup
Regenerative circuit wikipedia , lookup
Stray voltage wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Voltage optimisation wikipedia , lookup
Wien bridge oscillator wikipedia , lookup
University of Leicester PLUME Ref: PLM-PAY-LabElecsGain-014-1 Date: 02/10/2008 Finding the gain of the electronics chain P. peterson Date Updated Reference Number change 02/10/2008 PLM-PAY-LabElecsGain-014-1 first version issued Gain is defined as the ratio of an input voltage to an output voltage. It is very important to know the gain produced by the electronics chain under different conditions both for use of the multichannel analyser (MCA) and to calculate the size of the charge pulse when using the microchannel plate (MCP) detector body. The equipment used for this experiment is given in the “Equipment Configuration” document. This series of experiments calculates the gain for every component in the chain individually, but for the actual experimental setup with the MCP we transferred a lot of the signal processing electronics to a large NIM rack and significantly changed the chain components. Because this will likely interfere with the gain, the chain will need to be recalibrated after the initial testing of the MCP, and next time we will calibrate the chain as a whole, not component by component, to reduce error. Basically, we set the electronics chain up and use the pulse generator to send pulses through it, then connect one channel of the oscilloscope to one side of a component an the other channel to the other side. Then, we just compare the maximum height of the voltage spike on one side with its height on the other to get the gain. Preamp This is a charge-sensitive preamp, not a voltage amplifier, but we can simulate the MCP’s charge pulses by using the test connection of the preamp. This connection has a test capacitor which is used to convert the voltage pulses from the pulse generator into charge pulses which are then fed into the rest of the amplifier circuitry. [1] The preamp is also an inverting amplifier, which means that an influx of negative charges (electrons from the MCP) Page 1 of 4 University of Leicester PLUME Ref: PLM-PAY-LabElecsGain-014-1 Date: 02/10/2008 will produce a positive voltage spike. The oscilloscope readings taken from either side of the preamp are shown in figure 1. Figure 1 (Left): Pulser signal, (Right): Preamp signal The ratio of voltages were 3:0.9, so the voltage gain of the preamp is -0.3, for a voltage pulse with rise time 0.02µs and fall time 0.05µs. For longer voltage pulse times (1µs rise, 10µs fall) gain fell only slightly to around 0.28, but the amplified pulse duration was almost unchanged. The charge gain is determined in this setup by the test capacitor. For an ORTEC 118A preamp, the internal test capacitor has a value of about half a picofarad [2]. The 3V incoming signal was thus converted into a 1.5pC charge injection for the amplifier circuitry. This 1.5pC produced an output voltage spike with maximum magnitude 0.9V, and so the voltage/coulomb ratio of the amplifier is 1V out = 1.666pC in. Shaping amp The central component of the shaping amp is a CR-RC circuit. A detailed discussion of the characteristics of this circuit is referenced from the Payload wiki page. [3] The most important setting of the shaping amp is the rise time - a gradual rise is essential to allow the MCA to accurately analyse the peak voltage. The MCA can handle a rise time of half a microsecond, which is as low as the shaper will go. This is a good thing, as a longer rise time will lead to a lower gain. Another feature of the shaping amp's CR-RC circuit is the pole-zero effect. This manifests itself as a negative voltage peak that occurs after the initial positive peak. This phenomenon doesn't affect the ability of the MCA to record the height of the positive voltage peak, and can be ignored. Page 2 of 4 University of Leicester PLUME Ref: PLM-PAY-LabElecsGain-014-1 Date: 02/10/2008 The shaping amp has an internal signal amplifier, too. There’s a fine gain amplifier that can be set anywhere between 0.5x and 1.5x, and a coarse amplifier with discrete values of 20, 50, 100, 200, 500, and 1000x. The equipment is pretty old, and there’s a possibility that the actual gain of the amplifier has drifted away from its factory settings. A small experiment was done to examine this, described below. As before, the oscilloscope was connected on either side of the shaping amplifier. The readings are shown in figure 3. The attenuation of the pulse generator was changed to give a 3V output signal from the preamp, for maximum precision. The gain of the shaping amplifier was set to 10x. Figure 3 (Left): Preamp signal, (Right): Shaped signal The voltage gain of this configuration is 3:0.45, or 0.15x By examining the voltage gain produced by the different coarse gain settings on the shaping amp, we were able to determine the actual gain of each setting. Three runs were done to increase accuracy, as the oscilloscope used had significant ‘signal drift’ where the trace would distort over time. As you can see in table 1, they’re actually not that different. Listed Average Actual gain voltage (V) gain 1000 6 (reference) 1000 500 3.1 516.6667 200 1.263333 210.5556 100 0.603333 100.5556 50 0.310667 51.77778 20 0.131 21.83333 Table 1: Shaping amp gain Conclusion We now have enough data to determine the gain of the entire electronics chain for both voltage signals and charge pulses. Vout = -0.3 x 0.15 x 0.1 x Gshaper x Vin = 0.0045 x Gshaper x Vin (1) Vout = -6x10^11 x 0.15 x 0.1 x Gshaper x Qin = 9x10^9 x Gshaper x Qin Where Gshaper is the actual gain of the shaping amp given in table 1. Page 3 of 4 (2) University of Leicester PLUME Ref: PLM-PAY-LabElecsGain-014-1 Date: 02/10/2008 [1] Data recording and analysis - Pearson, Lees and Brunton (2003) [2] http://prola.aps.org/pdf/v29/i6/p3500_1 [3] http://solarwww.mtk.nao.ac.jp/kobayash/thesis/node37.html Page 4 of 4