I made a video showing my setup and posted it to YouTube here:
-What scope are you using?.
A little bit more about the set up: A TDS3052C is connected to see the square wave pulse (TX) and the transducer response (RX). Both channels on the Oscilloscope are used but I don't use the square wave pulse signal for calculations. The front of the square wave pulser is connected to a set of ultrasound transducers. This project involves using Shear Wave transducers and Longitudinal Wave transducers. Set up as is, I have to disconnect the two transducers and reconnect the two transducers to get readings from both types of transducers to calculate my end goal: porosity.
-1 second is the switching signal period you are willing to have or its ON state? In other words, what's the frequency and duty cycle you want for your switching signal?
My goal is to come up with some sort of digitally controlled switch for the low-attenuation coax wires. I want to be able to set a digital pin to HIGH and have the relay switch transducers. I said 1 second before but that was because I wanted to give a high number - that's how long I figured the circuit would need to stabilize after the switch. I'm not sure what the duty cycle/frequency should be, I was thinking no frequency/pwm just manually controlled via the Arduino w/ Javascript button/script (I'm using BreakoutJS (Firmata based Arduino control via HTTP)) and interfaced with the Tektronix over Ethernet so all that stuff is taken care of on the computer.
The square wave pulser is set to always be on.
-When you mentioned 2 pairs, I guess is 4 coax cables and you want to switch 2 at a time to the scope 2 Channels inputs. Is that correct?
-If that's the case, are all 4 wires carrying 400V pulses? or is 2 TXs and 2 RXs?
Right now, (I think) only one transducer/scope pulses with the 400V and the other one receives it and there is a significant amount of attenuation. I'm actually not sure if I'm qualified to answer this because I know the square wave pulser is set to 400V but the Oscilloscope only reads 5V (with the Gain and Voltage at maximum). Maybe whoever bought the set up planned it out like this? IDK but square wave pulse channel on the Oscilloscope does say Probe Comp = 5V Square Wave Sign on the input.
-What's the pulse repetition freq (PRF) of the signal?.
The PRF settings read EXT, 100, 200, 500, 1K, 2K, and 5K. I'm not really sure what this is used for but I was thinking this setting might be useful to find the mass of these pills.
-If you use relays, the bouncing on the contacts will introduce noise. If the switching is done too fast, as your ON/OFF time gets closer to the duration of the bouncing the signal to noise ratio will be greatly deteriorated.
Not a huge deal - hopefully this project works out and I'm given a bigger budget to use on v2. Again, it's not super important that I switch the sets fast, even up to 10 seconds switch time would be acceptable although the faster the better and I'm trying to do this right the first time around.
-If you switch 400V directly with relays there will probably be sparking in the contacts and you may need special HV relays to extend their life. Besides that you are risking damaging the scope input with such a HV.
Here's what I was thinking might be one way to go that -might- address this issue. Assuming the receiving transducers only receive a small amount of voltage, maybe I can just have one relay that controls the receiving transducers and then just split the transmitting line so that both of the transmitting transducers are always running.
-If you switch 400V directly with relays there will probably be sparking in the contacts and you may need special HV relays to extend their life. Besides that you are risking damaging the scope input with such a HV.
It'd be nice but I'm also trying to get this done cheaply (under $100)... I only need it to last.. let's say 2000 switches -- enough time to test it, show it to my advisor, and the possible grant provider.
It may be important to note that Oscilloscope and square wave pulser have Ext Trig and Ext Trig In - is this where I should be connecting a ground from the Oscilloscope to the square wave pulser? Also, here's a screenshot of the Oscilloscope response when the Square wave pulser begins a pulse showing that the Oscilloscope is reading both a maximum of around 5V for both signals when the gain is at max and the voltage is at max.
Thanks for the help.