# 3.3.1.32. NXmonitor¶

**Status**:

base class, extends NXobject

**Description**:

A monitor of incident beam data.

It is similar to the NXdata groups containing monitor data and its associated dimension scale, e.g. time_of_flight or wavelength in pulsed neutron instruments. However, it may also include integrals, or scalar monitor counts, which are often used in both in both pulsed and steady-state instrumentation.

**Symbols**:

No symbol table

**Groups cited**:

**Structure**:

@default: (optional) NX_CHARDeclares which child group contains a path leading to a NXdata group.

It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See https://www.nexusformat.org/2014_How_to_find_default_data.html for a summary of the discussion.

mode: (optional) NX_CHARCount to a preset value based on either clock time (timer) or received monitor counts (monitor).

Any of these values:

`monitor`

|`timer`

start_time: (optional) NX_DATE_TIMEStarting time of measurement

end_time: (optional) NX_DATE_TIMEEnding time of measurement

preset: (optional) NX_NUMBER {units=NX_ANY}preset value for time or monitor

distance: (optional) NX_FLOAT {units=NX_LENGTH}

DEPRECATED: Use transformations/distance insteadDistance of monitor from sample

range: (optional) NX_FLOAT (Rank: 1, Dimensions: [2]) {units=NX_ANY}Range (X-axis, Time-of-flight, etc.) over which the integral was calculated

nominal: (optional) NX_NUMBER {units=NX_ANY}Nominal reading to be used for normalisation purposes.

integral: (optional) NX_NUMBER {units=NX_ANY}Total integral monitor counts

type: (optional) NX_CHARAny of these values:

`Fission Chamber`

|`Scintillator`

time_of_flight: (optional) NX_FLOAT (Rank: same as field efficiency, Dimensions: same as field efficiency) {units=NX_TIME_OF_FLIGHT}Time-of-flight

efficiency: (optional) NX_NUMBER (Rank: same as field i, Dimensions: same as field i) {units=NX_DIMENSIONLESS}Monitor efficiency

data: (optional) NX_NUMBER (Rank: dataRank) {units=NX_ANY}Monitor data

sampled_fraction: (optional) NX_FLOAT {units=NX_DIMENSIONLESS}Proportion of incident beam sampled by the monitor (0<x<1)

count_time: (optional) NX_FLOAT {units=NX_TIME}Elapsed actual counting time, can be an array of size

`np`

when scanning. This is not the difference of the calendar time but the time the instrument was really counting, without pauses or times lost due beam unavailability

depends_on: (optional) NX_CHARNeXus positions components by applying a set of translations and rotations to apply to the component starting from 0, 0, 0. The order of these operations is critical and forms what NeXus calls a dependency chain. The depends_on field defines the path to the top most operation of the dependency chain or the string “.” if located in the origin. Usually these operations are stored in a NXtransformations group. But NeXus allows them to be stored anywhere.

The reference plane of the monitor contains the surface of the detector that faces the source and is the entry point of the beam. The reference point of the monitor in the x and y axis is its centre on this surface. The reference plane is orthogonal to the the z axis and the reference point on this z axis is where they intersect.

integral_log: (optional) NXlogTime variation of monitor counts

GEOMETRY: (optional) NXgeometry

DEPRECATED: Use the field depends_on and NXtransformations to position the monitor and NXoff_geometry to describe its shape insteadGeometry of the monitor

OFF_GEOMETRY: (optional) NXoff_geometryThis group describes the shape of the beam line component

TRANSFORMATIONS: (optional) NXtransformationsThis is the group recommended for holding the chain of translation and rotation operations necessary to position the component within the instrument. The dependency chain may however traverse similar groups in other component groups.

## Hypertext Anchors¶

List of hypertext anchors for all groups, fields, attributes, and links defined in this class.