Record Support
Table of contents
The std module provides three custom EPICS record types.
EPID Record
The EPID record is an enhanced PID (Proportional-Integral-Derivative) feedback record. It maintains a setpoint and adjusts an output based on the difference between a controlled value and that setpoint. Compared to the standard EPICS base PID record, the EPID record adds:
- Separation of device support from the record, allowing “Soft Channel”, “Async Soft Channel”, and “Fast Epid” device types
- Absolute output computation (not differential), enabling direct limit checking on the output
- Integral term limiting to prevent windup
- Drive limit fields (
DRVH,DRVL) and an output link (OUTL) built into the record - Support for asynchronous readback devices via trigger/callback fields (
TRIG,TVAL)
Throttle Record
The throttle record enforces a minimum delay between successive value changes sent to an output PV. It was created to protect devices that need time to stabilize after a change – for example, a laser delay generator that requires a settling period. If a value is changed faster than the configured delay, the record holds the latest value and sends it when the delay period has elapsed. Features include:
- Configurable minimum delay between output writes
- Optional drive limits with clipping
- Synchronization input for reading back the current target value
- Transparent operation when values change slower than the delay
Timestamp Record
The timestamp record captures the current time and formats it as a string. It provides eleven selectable format styles via the TST menu field, ranging from simple HH:MM to full date-time with nanosecond precision. Formats include US, European, VMS, and ISO-like styles. The record stores both the formatted string (VAL) and the raw seconds past EPICS epoch (RVAL).