I am constructing a system for controlling a pump by using the flow rate. The system consists of pump, flowmeter, cDAQ-9174, NI-9203, and NI-9266. The pump and the flowmeter are connected to NI-9266 and NI-9203, respectively, and both connections use electrical current of 4-20 mA. cDAQ-9174 is connected to a PC with a USB cable.
The problem is the electrical current from the flowmeter is around zero (order of micro ampere), according to MAX. I have checked the followings and have no idea what the cause is.
(1) The cause may NOT be inside the flowmeter. I connected the flowmeter with another system, which is composed of cDAQ-9178 and NI-9203 and is connected to PC through Wi-Fi. When the flow rate is zero, the electrical current displayed on MAX is around 4 mA. The higher the flow rate was, the stronger the electrical current was.
(2) The cause may NOT involve the connection between the flowmeter and the cable. Though the cable is used for both of flow rate transmission and power supply, the power is supplied to the flowmeter.
(3) The cause may NOT be inside the cable, for example the snapping of a wire. When I used another cable, the same problem occurred.
(4) The cause may NOT involve the connection between the wire and the analog input terminal of NI-9203. I tried unplugging and re-plugging many times.
(5) The cause may NOT be inside the analog input terminal of ai0 in NI-9203. I plugged the wire with ai1, and the same situation occurred.
(6) The cause may NOT be inside NI-9203. I have two NI-9203s, and when I used the other one the same problem occurred.
(7) The cause may NOT involve the connection between NI-9203 and cDAQ. I plugged NI-9203 with another slot of NI-9203.
(8) The cause may NOT be inside cDAQ-9174. The pump output can be specified and controlled with PC.
I have no idea what to do next and what the cause may be.