In split range control, we will control 2 outputs with time interval. Eg :(wit

In split range control, we will control 2 outputs with time
interval. Eg :(with 4-20 ma signal, for 4-12 ma we are
operating one control instrument like valve & for 12-20ma we
are operating other control instrumet (other valve). If we
get a signal of 15ma to first instrument (Valve 1), what
will happened to the first valve, and if we get signal above
20 ma to 2 valve what will happened ?

Question Posted / mohi

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In split range control, we will control 2 outputs with time interval. Eg :(with 4-20 ma signal, fo..

Answer / kyle condran

It depends on the setup the 2 above post both correct the following scenario can also be seen sometimes.

Valve 1 set for 4-12mA (100% open @ 4mA and 0% open at 12mA)
Valve 2 set for 12-20mA(100% open @ 20mA and 0% open at 12mA)

For example if you have a temperature control with 2 valves one controlling steam and one controlling chilled water, going into a heat exchange process, when we want to increase temp out of heat exhanger contol signal goes up towards 20mA chilled water valve closes and steam valve opens. when we want to cool the process down the opposite happens and the control signal falls towards 4mA the steam closes and chilled water valve opens.

so 4mA is full on chilled water 20mA is full on steam 12mA is both closed.

lets assume fail open cooling / fail closed heating valve.

as for 15mA on valve 1 depending on where the split range is done, ie controller or valve.

for our example if done in valve it will ignore anything above 12mA and be fully closed.
above 20mA in our example will be ignored by valve 2 since it is allready at 100% at 20mA.

see http://www.contek-systems.co.uk/Documents/split_range_control.htm for the first 2 post