Hello all,

I am having issues configuring a DataTaker DT82E-4 data logger that connects to a Toshiba GF630 flow meter. The output signal of the flow meter is 4 mA - 20 mA (corresponding flow rate 0 - 650 GPM). The flow meter has three wires: red (positive), white (negative) and green (ground). For wiring configurations, I used C3 - Independent Current Input using Internal Shunt (Red positive wire connected to the "#" analog channel 1 terminal, white negative wire connected to the "EXT #" terminal and ground wire unconnected). In dEX Configuration Builder I configured the logger to measure current using Channel 1, 4-20 mA Current Loop. In "Scaling" - "Span", the "Physical (Onput)" value was typed in as "0" and "650". In the "Measured (input)", I found that it had to be 400 and 2000. Does that mean that the measured value is voltage (4 mA X 100 Ω)? How come the manual says the return value is 0 and 100 percent? When I changed the channel type from "4-20 mA Current Loop" to "Current", it appeared the "Measured (input)" value has to be entered as "68" and "340." Isn't that supposed to be the input current which is "4" and "20"? Where does the magic number 17 (17 X 4 and 17 X 20) come from? The other issue is I found the measured flow rate by the data logger was slightly different from the reading by the flow meter. They were off by almost 0.5 GPM. What was causing the reading difference? Did I do something wrong when I configured the data logger?

Thanks in advance for your help! I really appreciate it.

Dewu Zhang

Hi Dewu,

Current loop channel is used to read 4-20 mA signal, it will have 0-100% as the output, 0% represent 4 mA while 100% represent 20 mA in the scaling.

However you can still use current channel to read 4-20 mA, it will have different declaration in the scaling. You will need to use the actual figure 4 mA and 20 mA.

And your question whether to use voltage figure in the scaling, the answer is no. Although the logger does sense voltage through (internal) shunt resistor, it will provide you with current output automatically through internal conversion.

The last one is about scaling figure that change when using/ changing current loop channel into current channel, you will need to rewrite the content of scaling figure.

One thing to remember when using internal shunt resistor, the resistor is separated by internal relay (the one you hear clicking) and it will only close (for 10 ms) when the channel is called/ due. For some sensor 10 ms may not be enough to establish the output, so you may need to increase measurement delay in the advance setting.

Best regards,
Rudy Gunawan