TC-08 Single Channel Terminal Board, measuring 0-5v

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Blake
Newbie
Posts: 1
Joined: Fri Jul 16, 2021 2:38 am
Location: Weyburn, Saskatchewan, Canada

TC-08 Single Channel Terminal Board, measuring 0-5v

Post by Blake »

Hi
I am a new user attempting to use a new USB TC-08 with single channel TC-08 Terminal board to measure 0-5vdc signal. My issue is that the value displayed on PICOLOG 6 shows ~1.5vdc when a clear 5vdc signal is applied to the input (+5vdc connected to the "4-20/5v" & earth connected to "COM", yellow switch "OFF")

The 5vdc signal is derived using a basic voltage divider resistor circuit to lower the voltage from 25vdc to 5vdc. R1=10kΩ, R2=2.5kΩ. R1is connected to +25vdc, R2 is connected to R1 in series and then connected to ground. With R1&R2 connected in series the +5vdc signal to the TC08 comes from the junction of R1&R2 while the "COM" is connected to ground at the same point as R2.

This set up is simply to familiarize myself with the TC-08 single channel terminal board. My real goal is to use a similar set up to log several 24vdc PWM 150hz inductive actuator circuits, in addition to 0.5-4.5vdc signals from pressure transducers.

I have tried restarting my computer, rebooting Picolog 6, reinstalling picolog 6, trying different channels on the TC-08, trying other single channel terminal boards & trying other TC-08 USB dataloggers. I have verified the signal voltage with 2 meters, used other much lower Ω and much higher Ω resistor combinations to achieve between 3-5vdc signal but the display reading is always quite low compared to my meters.

I appreciate any assistance you can offer. Thank You.

Gerry
PICO STAFF
PICO STAFF
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Joined: Mon Aug 11, 2014 11:14 am

Re: TC-08 Single Channel Terminal Board, measuring 0-5v

Post by Gerry »

Hi Blake,

We apologise for the delay in answering your post (there has been a lot of other work that needed attention).

So, in the event that you are still looking for an answer to your question, The Terminal Board adapter for the TC-08 already uses a resistor divider to divide down the voltages of the different Voltage inputs. So your resistor Divider is creating an incorrect combination of resistor values for 5V. If you are going to use a resistor divider then you need to use the 5V input as a bottom leg of the divider providing 5V with a resistance of 101kΩ. So, to divide your 25V down you would need a top leg (resistance in series with the 5V input) of value 404kΩ for 1% accuracy (so 402kΩ in series with 2kΩ, at 1% tolerance).

Regards,

Gerry
Gerry
Technical Specialist

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