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6.3.5 No Pulse Received at PLC or FMS
If your RT40 is correctly displaying a flowrate and total but you are not receiving a pulse
signal at your PLC, fuel management system, or any other device with a frequency input, this
may be due to a fault at either the RT40, the external device, or incorrect/broken wiring. To
troubleshoot this fault please follow the below steps.
1. If your RT40 is not counting volume on the Total screen, and/or not displaying a
flowrate reading, please first refer to sections 6.3.1 and 6.3.2
2. Enable the “test output” function in the diagnostics menu (see section 6.1.4). If
enabling this function causes the PLC/FMS to begin receiving pulses, then there is
possibly a fault with the RT40, or it is possible the input frequency of the PLC is
limited. Make sure you are using a Scaled Pulse Output and try reducing the
resolution of the output pulse until the PLC is able to read the signal (see section
5.8.2)
If the RT40 is correctly displaying a total and flowrate, and the “test output” function does not
cause the PLC/FMS to begin receiving pulses, then we must validate the output of the RT40
with another device.
3. If a second RT40 is available; disconnect the wiring from the RT40 to the PLC or FMS.
Then connect the output terminals of your RT40 to the input terminals of the
diagnostic RT40 using short lengths of wire. With the diagnostic RT40 configured
with a HALL input signal, go to the Input Frequency diagnostics menu on the 2
nd
RT40. If the 2
nd
RT40 is displaying a reading of 10Hz then your original RT40 is
functioning correctly, and your fault is with the PLC/FMS or the wiring.
4. If a 2
nd
RT40 is not available, a digital multimeter with a frequency(Hz) setting is a
suitable alternative. If after conducting these measurements directly on the output
terminals of the original RT40 you cannot measure a frequency of 10Hz, then there is
a fault with the RT40. Please contact FLOMEC technical support.
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