Is it possible to do the stroke test of the control valve without using 250 OHMS

When doing stroke check of control valve in field and no power from panel We need loop calibrator Hart nitrogen cylinder Question is if we need 250 ohms or not? Will HART work With 250 ohm or without 250 ohm?

Only stroke check means you will have source 4-20mA from loop calibrator (Eg: Fluke 705). No need for an external resistor.

Don’t require any resistance (250 ohms) in Emerson 475 hart …when you are using old hart like Emerson 375, Yokogawa or ABB 805 then you should connect 250-ohm resistance…

  1. 250 ohm resistor required?

It depends. Most 2 wire, loop powered smart positioners using HART have an internal resistance > 250 ohms. An example is Siemens PS2 positioner that develops 330 Ohms at 20mA.

But the 3-4 wire model has only 10 ohms of resistance on the analog input and would need an external 250 ohm resistor to work with HART.

So the 2 wire model has sufficient resistance for the HART signal to operate from a HART signal from a HART master, like a handheld or a laptop with a HART modem, but the 3-4 wire models do not.

  1. No power from the panel I don’t understand the ‘no power from the panel’ statement.

A 2 wire loop powered positioner needs power from its analog input signal to operate. A 3-4 wire positioner needs external power to operate.

Any test that cuts power to the positioner will not produce a positioner-initiated partial stroke test.

If the area is general purpose, not a hazardous area, a portable pack of a set of three 9V batteries wired in series will power any loop powered device, but a battery pack is an arcing/sparking ignition source and can’t be used in a hazardous area.