I would like to ask about the issue of current measurement for positioners

I don’t know about this type of locator, but I do know the current value; they need to be connected in series, and the current in each series connection must be equal.

As I understand it, in theory it’s not possible to measure current anywhere simultaneously, but in practice I have measured it while using a mechanical positioner; a quick measurement is also feasible. As for the positioner you mentioned, I’m not sure about that

Current measurement always requires series connection. Some instruments have current testing terminals in the junction box, allowing for direct measurement of current. There is a resistance between its test terminals, and the internal resistance of the ammeter is much smaller than the parallel resistance, so the current can be measured directly.

Using the ammeter function of a multimeter to measure current at the terminals will not damage the multimeter or cause a short circuit in the controller that leads to valve operation, but this method should not be used for current measurement. Current must be measured in a series configuration, as the current is equal throughout a series circuit; in parallel circuits, however, the current is divided up.

The multimeter will not be damaged, but the proper operation of the control valve will be affected; this method of measurement is not suitable.

Don’t do it just to save trouble; some tasks are simply very time-consuming, but haven’t we always done things this way over the years?

This post was last edited by feng*aosa on 2015-6-18 at 18:24. To measure current accurately, it is necessary to connect the measuring instrument in series with the circuit. However, under specific conditions and when the requirements for measurement accuracy are not high, it is possible to avoid direct series connection. 　　An ammeter is an instrument with very low input impedance. If it is connected in parallel across the load of a voltage source, it is equivalent to short-circuiting the voltage source; as a result, not only cannot the current under normal operating conditions be measured, but losses may also occur and even physical injury can be caused. 　　If it is connected in parallel across the load of a constant current source, it is as if the load of the constant current source has been short-circuited; however, since a constant current source supplies the power, the current will remain at its original level to some extent even when the load is short-circuited. 　　The signal current of the locator comes from the control room, and in order to accommodate different actuating devices, this signal current is provided as a constant current source. If an ammeter is connected in parallel across the load, due to the high resistance of the load (between 250 and 500Ω) and the low input resistance of the ammeter (which does not exceed 1Ω), the majority of the current from the constant current source flows through the ammeter, thereby reflecting the output level of the constant current source. 　　The results obtained in this way will be inaccurate. Firstly, the current division ratio between the load resistance and the input resistance of the ammeter affects the measurement results; Secondly, the precision of the constant current provided by the signal from the control room is generally not very high, and changes in the load will alter the value of the output current. 　　Therefore, it is possible to connect an ammeter in parallel at the signal terminal of the positioner to measure the magnitude of the signal current, but there will be errors. It is particularly important to note that during measurement, the signal current flows through the ammeter rather than passing through the positioner, causing the positioner to act as if the signal is disconnected. Therefore, this method is not usable during the production process. 　

It was tested this way before, and it was possible to measure the current; however, the valve would move. It’s best to disconnect the valve and perform the measurement in series.

If I remember correctly, it’s possible, because it has test terminals. It’s not possible if there is no test terminal.