Situation I've found regarding a measuring taking place in a plant -

Using CTC AC 102-1A transducers and a CSI 2120 data collection box. With the CSI having a bias voltage of 12V and the said transducer specifications of 18-30 volts, what the odds the data are 100% valid?

I would think an external power supply would be needed: yea or nay? I have both 18V and 27V pwr supplies would the fringe of 18V be adequate 100% of the time? Or, please give opinion. Thank you.

Sam,

The CTC accelerometers will work perfectly with the CSI 2120, which is designed to work with ICP-type accelerometers.

Let me explain how this system works.....

ICP-type accelerometers use a constant current power supply. The data collector has a constant current source with two important parameters: 1) the current supplied & 2) the maximum voltage available. The current supplied is usually between 2 - 5 mA, with a maximum voltage of 18 - 24.

The bias voltage is controlled by the accelerometer. It uses the current supplied by the data collector and biases the current to around 12 volts. The AC component of the signal (the acceleration) rides on top of this ~12 volt bias voltage. The combined signal level + bias voltage can't be less than 0 nor higher than the maximum voltage supplied by the data collector (actually, the range is a little smaller as some head-room is needed on each end).

Lets say we have a 50 g peak sinusodial signal. With a standard 100 mV/g accelerometer, this signal would range from -5 volts to +5 volts. When this rides on the bias voltage, the signal level the data collector will see ranges from 7 volts to 17 volts.

You can verify that the data collector has a standard ICP-type power supply pretty easily. First, connect a voltmeter across the inpput without an accelerometer connected. You should measure between 18 - 27 VDC.

Next, switch to the DC mA scale and measure the current across the input connector. NOTE: this should only be done with a constant current supply! You should measure arouind 2 - 5 mA.

Finally, connect an accelerometer and measure the DC voltage across it. It should be around 12 volts. This will vary between accelerometers, particularly between diffrent manufacturers and models.

If I can be of help, please call. Spintelligent Labs is a CTC reseller.

Jon
Spintelligent Labs
206-855-9284

Only problem I ever had is when going under 2mA, if you for some reason supply only like 1mA some brands make it and some don´t, so supply at least 2mA for normal cable length and it works. Olov

Sam,

The manual for my 2120 specifies a 2-ma current source at a nominal 20-volts. It states that full scale input with Sensor Power On is +/- 9 volts and that corresponds to +/- 90 g's when using a 100-mv/g accelerometer. Many 100-mv/g accelerometers are limited to 50 g's.

Where did you get the 12-volts?

Walt

Thanks for the input - All,

I am aware that the CSI is powered via 12V batteries but was unaware that it supplied anything other than 12V. Thanks for your time Walt.

If the CTC accepts 12V why does it specify 18-30V? But, Jon's explaination is great. Again, thanks for the input; I have to have an outside opinion to remove bias. I also get this from folk regarding alignment, "oh, we need a different opinion, you're bias to your opinions as you've written a book on the subject". Maybe they should interview the guy on the street and go with popular opinion.

It (12V) may be the bias voltage set by the transducer, if you supply 24VDC 12VDC is halfway down. If you have 20 VDC and a transducer that give 10VDC bias it match +-90g swing giving some margin for the amplifier not going rail to rail but only +-9V. When the transducer takes it´s 2mA constant current the bias voltage will end up somewhere, partly pending on transducer brand, in the span 8-14 volts to give the extremes I think I seen with various combinations. Olov

Thanks Oli,

It's good to have people like you, Jon, Walt and many more (a lot) to have as a resource and take time to respond. I certainly appreciate the many that have taken time to respond over the years. Hat off or I would if the glare wouldn't bother you.