Hi, 2 questions for you.

1. Configuring a current probe, the type that clamps around the power cable like a clothes peg. The output is 1mV per amp (I'm measuring up to 42 amps). The signal is a fixed frequency (looks like 50Hz) and the signal is the variation of the peak to peak voltage. I'm not getting a consistent reading. How should I wire this to the DT800 (I am connecting the 2 cables to the + and - in channel 1) and how do I configure delogger?

2. I have pressure transducers with a variable current output(4 to 20 mA). I have connected a 100 ohm resistor across each transducer and measure the variable voltage across each resistor. The signal current also feeds to a PLC. The 100 ohm resistor seems to have modified the signal to the PLC where incorrect values are now being shown. Is there a way to configure this set-up so I do not have to reset the PLC.

Many thanks for any help,
Nick.

Good morning Nick,

1. Be careful using current transformers. Connect it up to the dataTaker before connecting to the cable to measure the power. CT can generate several hundreds of volts which can do all sorts of damage to you and the dataTaker. Read the channel using the VAC channel type, this will give you the RMS value of the current reading.

2. I need to know a little more about your setup.

   a. What load can the pressure transducer drive? Some of the older devices could only drive a maximum of 600 Ohms. The PLC is probably using 500 and your 100 Ohm may be marginal.

   b. How do you have them wire up, in series or parallel? Is the DT800 before or after the PLC?

Cheers

Roger

Hi Roger,

Ref question 1) You suggest connecting to the dataTaker before connecting to the cable to measure the power. However, if the CT can generate several hundreds of volts, will this damage the dataTaker?
I've scanned the manual, but am confused as to what a VAC channel type is. Would you kindly amplify on your explanation.

Ref question 2) We appear to have resolved this issue. We have put the 100 ohm resistor in series with the transducer and read the voltage across the resistor. Many thanks.

Nick.

Hi Nick,

I don't know your level of knowledge of electronics so please forgive me if I cover topics you already know. The forum is also for other to learn as well.

1. No 1 Part 1 - CT's
   I don't know exactly what device you have or if it has any electronics in it but a straight current transformer if left open circuit will generate several hundreds of volts and the ones I have worked with come with a warning to ceither connect them up first or to short out the leads if disconnected. Once they are connected to the logger then they are fine to read into and won't damage the dataTaker. I was just giving you a warning to be careful.

2. No 1 Part 2 - VAC v's VDC.
   A DC voltage measurement is quite simple, you just take one measurement, but an AC voltage cycles plus and minus around zero volts, so the voltage reading will vary depending on when the reading is taken. To get around this VAC is measured as RMS voltage (Root Mean Squared) Basically you take a whole heap of DC samples very fast and the calculate the RMS value from that.

3. No 2 - Current Transducers.
   The wiring of these transducers is best done as a serial connection. If you try connecting in parallel you most often have impedance mismatching between the two acquisition systems.

Cheers,
Roger

I think we are on the right track now. Many thanks for your help. BTW, I appreciate explanations from grass roots level (I'm a mechanical engineer}

Nick.