Valve Setting

Hi, If the positioner is set up properly there is no need to go below 4mA to close an air to open valve.Thank you

Usually 3.8mA is the lowest I would go. Tight shutoff is achieved by actuator size and trim. Having your input current drop that low might be bad for the positioner as some need more current than that to operate; this could be why you are having troubles with your display.

I have been realize tens of level control systems with boilers but have not seen an output current below 3,5mA from a controller.

Controllers supplies current 4-20mA provided that the load resistance is lower than 750 Ω generally.

However there is controllers that can accept 200Ω load only!. If controller you used is in this kind then measuring 2,4mA is not a surprize.

As a result the problem is if the "input impedance of actuator" bigger than the "rated value of controller's load impedance".

If this is not the case then you must check the lines of output loop of controller. There might be weak connection(s) anywhere in the loop or actuator's input gets defect.

good luck...

Actually there is no need to go below 0%. But in actual practice the actuator may not closing properly and hence some experieced person might have set the same closing at -10% which would be the actual value of 0%

Agree with wrenchpuller

As the level in tank increases output decreases.When output reaches 0%(4 mA) the valve should be shut full.

If controller output goes below0 % that shows the valve has not shut properly and the level is increasing.

Please check postioner calibration