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 controller in MODBUS communications mode (see here to change), 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.