A pressure controller for use in operating parallel reactors, the pressure controller including a reference pressure controller, the reference pressure controller including: a first restrictor channel, a second restrictor channel, a fluid passage, which fluid passage extends between the outlet of the first restrictor channel and the inlet of the second restrictor channel, a pressure control fluid source being adapted to provide a flow of pressure control fluid, having an entrance pressure at the inlet of the first restrictor channel and an exit pressure at the outlet of the second restrictor channel, the flow of pressure control fluid experiencing a first pressure drop Δρ1 over the first restrictor channel and a second pressure drop Δρ2 over the second restrictor channel, a connector connecting the fluid passage to the control chamber, the pressure control fluid at the connector having an intermediate pressure, the intermediate pressure being determined by the ratio between the first pressure drop Δρ1 and the second pressure drop Δρ2, a controllable thermal device, the thermal device being adapted to heat and/or cool the first restrictor channel and/or the second restrictor channel, therewith influencing the ratio between the first pressure drop Δρ1 and the second pressure drop Δρ2.