Automatic Needle Valve Controller

Introduction

This is controlling the flow of helium in a cryostat, via a needle valve, based on a lookup table implemented in the hardware.

The underlying hardware is a Eurotherm (Modbus) controller, and automaticNeedleValve.db adds some extra settings on top. This controller uses the 'Automatic Needle Valve Controller' OPI in IBEX.

The needle valve operation revolves around two modes: manager mode and setpoint mode.

The latter has the two modes 'Automatic' and 'Manual', which dictate the behaviour of the needle valve:

• Automatic mode:
  • Temperature (TEMP) is writable and readable
  • Flow (MANUAL_FLOW) can only be read
• Manual mode:
  • Flow (MANUAL_FLOW) is writable and readable
  • Temperature (TEMP) can only be read

Note: the above assumes manager mode is enabled; items are only writable in manager mode.

Main records

automaticNeedleValve.db

PV	Description	Access
FLOW	"Flow" Flow readback from transducer	Read only
VALVE_DIR	Valve Direction; 0 = Closing, 1 = Opening	Read only
FLOW_SP_MODE_SELECT	Flow Setpoint Select; 0 = Auto setpoint mode, 1 = Manual setpoint control	Read/Write
MANUAL_FLOW	Manual flow setpoint; Reliant on FLOW_SP_MODE_SELECT being at 1 (i.e. Manual)	Read/Write
FLOW_SP_LOWLIM	Low setpoint limit for flow control	Read/Write
NEEDLE_VALVE_STOP	Ability to 'inhibit' Loop 2	Read/Write

Other

PV	Description	Access
TEMP	Temperature readback from Eurotherm	Read/Write

Access control architecture

There are two mechanisms at work controlling SP access rights here; setpoint mode and manager mode.

Manager mode

All setpoint PVs have the field field(ASG, "MANAGER"), so all writable items are only accessible when manager mode is enabled (e.g., $(P)CS:MANAGER=1).

Setpoint mode

As detailed above, the access rights to the PVs MANUAL_FLOW and TEMP are also controlled via setpoint mode.

These rights are managed via a series of fanout/seq records, which set 0 or 1 to the .DISP field (see EPICS: Fields Common to All Record Types) of each of these PVs, depending on the mode:

	Auto	Manual
Flow	.DISP=1	.DISP=0
Temperature	.DISP=0	.DISP=1

See below for an explicit summary of the write access of these two PVs under both modes.

MANUAL_FLOW

	FLOW_SP_MODE_SELECT=0 (Auto)	FLOW_SP_MODE_SELECT=1 (Manual)
CS:MANAGER=0 (Off)	Read only	Read only
CS:MANAGER=1 (On)	Read only	Readable & Writable

TEMP

	FLOW_SP_MODE_SELECT=0 (Auto)	FLOW_SP_MODE_SELECT=1 (Manual)
CS:MANAGER=0 (Off)	Read only	Read only
CS:MANAGER=1 (On)	Readable & Writable	Readable only

The use of cainfo may be useful for troubleshooting to check read/write permissions.