Admesy hera Operating Manual - User Manual

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hera

spectrometer

operating manual

Contents

Introduction .......................................................................................... 3

1.1

Hera ............................................................................................. 3

1.2

Hera highlights ............................................................................ 3

1.3

Standards .................................................................................... 3

Interfaces ............................................................................................. 4

2.1

USB interface .............................................................................. 4

2.2

Ethernet interface ........................................................................ 4

2.3

RS232 interface .......................................................................... 4

2.4

Trigger in/out ............................................................................... 5

2.5

Power connections ...................................................................... 5

Communications protocol .................................................................... 6

3.1

USB ............................................................................................. 6

3.2

RS232 ......................................................................................... 6

3.3

Ethernet ....................................................................................... 6

Device drivers...................................................................................... 7

4.1

USB ............................................................................................. 7

4.2

RS232 ......................................................................................... 7

4.3

Ethernet ....................................................................................... 7

Command set description ................................................................... 8

5.1

Commands .................................................................................. 8

5.2

Command structure ..................................................................... 8

5.3

System commands ...................................................................... 9

5.4

Configuration commands ............................................................ 9

5.5

Measurement commands .......................................................... 11

5.6

User EEPROM commands ....................................................... 12

5.7

Returned results ........................................................................ 15

Measurement example ...................................................................... 16

Autoranging ....................................................................................... 17

7.1

Introduction ................................................................................ 17

7.2

How autoranging works ............................................................. 17

7.3

Auto-range parameters ............................................................. 18

7.4

Auto-range in practice ............................................................... 18

7.5

Programming Hera for auto-ranging ......................................... 19

7.6

Auto-ranging recommendations ................................................ 19

Hera measurement results ................................................................ 20

Operating modes & triggering ........................................................... 20

1 Introduction

1.1 Hera

The Hera spectrometer series consist of various types of spectrometers.
VIS spectrometers ranging from 380 to 780nm (Hera 01), and 360 to
830nm (Hera 02) and UV-NIR with a range of 200 to 1100nm (Hera 04).

The Hera series is available in a variety of optical systems: 5, 10 or 20mm
collimating lens or a 1cm

cosine corrector. For measurements of light

sources Admesy offers a range of integrating spheres which can be
connected through M8 fibre connections. A fixed position fibre connector
has been developed to connect the optical fibre in a fixed and uniform way
from calibration to final use. Due to this fixed position measurement results
are more stable. This manual covers all Hera models. Where applicable, it
is indicated for which model a command is valid or not.

1.2 Hera highlights



Various spectral ranges



Numerous optical configurations including lens based systems,
cosine corrector and fibre optics for remote use (e.g. integrating
spheres)



Auto-range function



Excellent linearity



Dark current compensated



All spectral calculations and compensations are done inside the
device



USBTMC compliant, SCPI command set, high speed device



Directly supported in Labview / Labwindows / Visual Studio via
VISA library. Other programming languages that support VISA can
be used



Numerous interfaces, ideal for system integration

1.3 Standards

The  Hera  is  compliant  to  the  USBTMC  standard  and  can  be  used  in
combination  with  external  provided  USBTMC  compliant  drivers.  Currently
it  has  been  tested  on  Windows,  Linux  and  Apple  OSX  using  NI  VISA
(www.ni.com/visa)  and  using  the  open  source  drivers  on  Linux  (i686,
x86_64 and ARM).

2 Interfaces

2.1 USB interface

The  USB  B  connector  is  used  to  connect  the  Hera  to  a  PC/Laptop.  The
Hera uses the USBTMC class protocol and can therefore be used directly
with  third  party  provided  VISA  compliant  libraries  like  NI-VISA.  Hera  can
be used USB powered in case the host provides enough current. Normally
every  host  should  be  able  to  drive  500mA,  but  not  all  of  them  do.  Also,
USB-HUBs  mostly  do  not  supply  enough  current.  It  is  therefore
recommended to use powered USB-HUBs only.

2.2 Ethernet interface

Ethernet  of Hera  is 100Mbit and is  10Mbit/GigE compatible. Ethernet can
be  used  in  the  same  way  as  USB.  All  commands  have  the  same  format.
Ethernet  is  preferred  over  USB  in  situations  where  the  distance  between
device and a PC are more than 5 meters.

2.3 RS232 interface

RS232 is provided to connect the Hera to any host that doesn't provide
USB or Ethernet or for which no USBTMC drivers exist. Using RS232, the
functions that generate a lot of data (spectrum) are still available, but the
use of it is highly discouraged due to the low speed of RS232.

Baud
rate

Data bits Parity

Stop bits Flow

control

Termination
character

115200¹

None

LF=’\n’

Table 1 RS232 port configuration.

1 Baud rate can be changed.

Fig 1 Hera RS232 connection.

Fig 2 Rear side mini-DIN-6 pin connector.

2.4 Trigger in/out

The Hera has two trigger connections. One trigger output and one trigger
input.  The  connectors  are  SMA  connectors.  When  triggering  is  enabled,
the trigger output line will be set to a high level once the measurement has
finished and the measurement result is available. It will stay at a high level
until  the  next  command  is  carried  out,  but  has  a  minimum  high  level  of
5μs. A trigger will carry out the last send command and send the result to
the host via the selected interface. The colorimeter main application allows
external  triggering  in  the  data-logging  tab.  Supplied  code  examples  show
how to use this feature in an application. The trigger output line is used to
indicate  that  the  measurement  is  ready.  Trigger  signals  should  comply  to
the following timing (Fig 3).

Fig 3 Trigger-in timing.

Trigger pulses arriving faster than the Hera can measure will be ignored,
but it may slowdown overall performance. Trigger pulses should not arrive
faster than the measurement takes to complete. The best way is to use the
trigger output to make sure measurement was finished.

The trigger out port provides a continuous high signal when the device is
in use. Its signal turns low when the device is not executing any
commands.

2.5 Power connections

The Hera should be connected to USB with sufficient power or using a 9V
DC  power  supply  to  the  RS232  connector.  When  using  RS232  the
spectrometer  needs  to  be  powered  via  the  external  adapter.  This  can  be
done  through  the  mini-DIN  connector  as  illustrated  in  the  RS232
connections.  The  unit  shall  be  powered  by  a  9V  DC  voltage  or  via  a
standard  USB  PC-port,  reinforced  separated  from  Mains,  with  a  limited
energy of < 150VA and < 8A.

Connection

Min.
Voltage

Typ.
voltage

Max.
voltage

Max
current

USB powered

4.75 V

5.00 V

5.25 V

350mA

DC powered

8.50 V

9.00 V

15.00 V

350mA

Table 2 Power supply levels.

𝑡 > 5

𝜇𝑠

3 Communications protocol

3.1 USB

The Hera can be connected to any USB host and is a USBTMC compliant
device  which  is  a  standard  USB  class.  Device  drivers  for  this  class  are
available  for  most  popular  operating  systems  (also  embedded).  This
makes  the  Hera  directly  usable  in  popular  programming  languages  like
NI's  Labview  and  Labwindows  but  also  C++,  Visual  basic,  C#,  Java  etc.
The  Hera  has  two  interfaces  build  in,  which  require  a  different  device
driver to be used.



Hera bootloader
(USB RAW device driver, Vendor ID: 0x23CF, Product ID 0x0105)



Hera01
(USBTMC device driver, Vendor ID: 0x23CF, Product ID 0x1021)



Hera02
(USBTMC device driver, Vendor ID: 0x23CF, Product ID 0x1022)



Hera01
(USBTMC device driver, Vendor ID: 0x23CF, Product ID 0x1023)

When the Hera is connected to the host, it will start the Hera firmware. As
soon as the firmware is idle to receive commands, the Power LED goes to
the ON state. The Admesy bootloader is a RAW USB device and in order
to use this device in Windows, a driver must be installed which is supplied
by  Admesy.  Besides  upgrading  to  new  firmware,  it  is  also  allowed  to
downgrade firmware in case this is required. Note that older firmware also
may require the use of older software libraries and/or executable versions
of  software.  The  Hera  is  USBTMC  compliant  and  can  be  used  with
libraries that contain a USBTMC compliant driver like NI-VISA. The Hera is
a  USB  2.0  Full  speed  device.  In  case  a  USB  host  is  detected,  it  is
assumed that the Hera operates only via USB.

3.2 RS232

Hera commands are equal for all interfaces. Note that for high speed
transfers it is best to use USB. When RS232 will be used, the device mode
should be set to RS232. This is done via software and stored in the device
EEPROM memory.

3.3 Ethernet

Hera commands are equal for all interfaces. When the Ethernet
connection will be used, the device mode should be set to ETH (Ethernet).
This is done via the Iliad application software: Device



Start-up

settings



Hera and stored in the device EEPROM memory. In the start-up

menu the IP address, gateway and network mask can also be changed.

4 Device drivers

4.1 USB

The following table shows an overview of USB support on various
operating systems.

NI-VISA

Libusb

Native
kernel

Agilent
USBTMC

Windows XP

Not
available

Not tested¹

Windows
VISTA

Not
available

Not tested¹

Windows 7

Not
available

Not tested¹

Windows 8(.1)

Not tested¹

Not
available

Not tested¹

Windows 10

Not tested¹

Not
available

Not tested¹

Windows CE

Not tested¹

Not
available

Not tested¹

Apple

OSX

PPC

Not tested¹

Not
available

Unknown

Apple

OSX

Intel

Not tested¹

Not
available

Unknown

Linux

i386

(32bit)

Linux

i386

(64bit)

Linux ARM

Not
available

Linux other

Not
available

Table 3 Supported operating systems.

1 Not tested: Available, but not tested by Admesy, 2 Native Kernel: Driver included with OS.
2 Windows XP SP3 is supported: Windows official support has ended as of April 8 2014

Admesy  supports  all  tested  platforms  but  does  not  provide  standard
applications  on  all  platforms.  The matrix  is  provided  to  show  the  possible
platforms  for  software  development.  Admesy  does  however  provide
software  examples  for  most  of  the  tested  platforms.  Most  of  these
examples can be found on our support web page.

4.2 RS232

When no USB driver is available or the host system does not provide USB,
RS232 can be used as it does not require additional drivers for the Hera.

4.3 Ethernet

No special drivers are needed for Ethernet operation. The Hera can be
directly addressed through a TCP/IP socket on port 10000. In case
firewalls are used, the TCP/IP port needs to be opened.

5 Command set description

5.1 Commands

The functions of the Hera can be best described via the following
categories.



System commands



Configuration commands



Measurement commands



User EEPROM commands

The Hera uses SCPI like commands for control and measurement. These
are ASCII based commands and follow specific rules regarding syntax.
Although the Hera uses SCPI like commands, they deviate from the SCPI
standard.

5.2 Command structure

Every  command  starts  with  a  colon  “:”,  which  identifies  the  root  of  the
command tree. Each further keyword is also separated by a colon. In case
parameters  need  to  be  specified,  the  last  keyword  and  parameters  are
separated by a single space character. In case more than one parameter
needs to be specified, the parameters need to be separated by a comma.

The command tables show commands in long and short format. The short
format is specified by upper case characters. It is allowed to use long and
short format or a mixed format. Optional keywords are shown between
brackets [...]. Commands are not case sensitive, so it is allowed to use
both or a mix of upper and lower case. The command structure is valid for
all communication interfaces of the Hera. It is recommended to terminate a
command by a newline character “\n”.

Command table

Valid command
syntax examples

Notes

:SENSe: INT 50000

:sens:int 500000
:sense:int 500000
:SENS:INT 500000
:SENSE:INT 500000

Sets the integration
time of the Hera

:MEASure:XYZ

:measure:XYZ
:measure:xyz
:meas:XYZ
:MEASure:XYZ

The measure
commands use the
averaging and
integration time
parameters that have
to be set first

Table 4 Example commands.

5.3 System commands

The following commands can be used to control the Hera or read back
information.

Command syntax

Parameters

Purpose

:*CLS

None

Clear status

:*IDN?

None

Identification query

:*RST

None

Reset Command

:*STB?

None

Read Status Byte query

:*TST

None

Self-test query

:*FWD?

None

Firmware date query

:*FWT?

None

Firmware time query

:SYSTem:VERSion?

None

Get system version
information

:SYSTem:ERRor?

None

Retrieve the last occurred
error

:SYSTem:ERRor:NEXT?

None

Retrieve previous errors

Table 5 System commands.

The Status byte can be used to retrieve information about the status of a
command or the system. Return values of the status command can be
seen in the table below.

Code

Description

System is idle

Data is available

Command processed

Data in buffer (should not occur)

An error occurred Use “:SYSTem:ERRor?”
to get the exact error that occurred

Table 6 Status commands.

Note:  The  status  and  error  commands  should  not  be  used  in  standard  programs.  They  are
not  necessary  when  programming  has  been  done  correctly.  They  are  available  in  case  a
problem  occurs  during  development.  The  :*RST  command  is  also  not  necessary  in  normal
programs.  It  is  advised  to  use the  :SENSe  and :CONF commands  in case  the  behaviour  of
the Hera needs to be changed to its default settings.

5.4 Configuration commands

Configuration commands are used to set parameters of the Hera that  are
used  by  the  measurement  functions.  The  settings  are  used  globally  by
other  measurement  functions.  The  selected  white  standard  is  used  for
dominant  wavelength  calculation.  The  integration  time  setting  can  be
varied  from  2.5ms  to  20s.  It  is  specified  in

μs. Results from the Hera

include  a  clip  and  noise  indication  which  indicate,  whether  the  measured
light  is  too  bright  (clip)  or  too  low  (noise).  When  clipping  is  detected,  the
resulting colour  will not be  correct and a  lower integration time should  be
chosen.  When  noise  is  detected,  a  larger  integration  time  should  be
chosen, see table 7 on next page.

Command syntax Parameters

Range

Purpose

:SENSe:INT

Int time

2500

–

20000000

Set integration time
(

s) of the

spectrometer

:SENSe:INT?

None

Returns the current
integration time setting
of the spectrometer

:SENSe:
INTERPOL

Interpolation
method

0 = linear
1 = cosine
2 = cubic
3 = Catmull-
Rom
4 = Hermite

Set the spectrum
interpolation method

:SENSe:
INTERPOL?

None

Returns the current
interpolation method

:SENSe:SP:
AVERage

Averaging

– 200

Set the averaging for
the spectrometer

:SENSe:SP:
AVERAGE?

None

Returns the averaging
setting for the
spectrometer

:SENSe:
RESolution

Resolution

0 = 0.5nm
1 = 1nm
2 = 2.5nm
3 = 5nm
4 = 10nm

Set the spectrum
output resolution.
Interpolation is done
using the earlier
selected method

Command syntax Parameters

Range

Purpose

:SENSe:SP:SBW

Calibration
matrix

“off” or
“user”

Set calibration matrix
for the spectrometer

:SENSe:CAL

User cal

0/1

Activate or deactivate
user spectrum
calibration

:SENSe:MODE

Mode

0 = USB
1 = Ethernet
2 = RS232

Set operating mode
(note, this one is not
stored in EEPROM).
This is useful for
triggering only

:SENSe:MODE?

None

Returns the current
setting

:SENSe:TRIG

Trigger

– 1

Set trigger mode (note
this is note stored in
EEPROM)

:SENSe:TRIG?

None

Returns the current
setting

:SENSe:TRIGDEL
AY

Delay

0 - 30000000

Configures a delay
before triggering in
microseconds

:SENSe:TRIGDEL
AY?

None

Reads the configured
delay before triggering

:SENSe:
AUTORANGE

Auto-range

– 1

Set auto-range mode

:SENSe:
AUTORANGE?

None

Returns current setting

Table 7 Sense and configuration commands.

5.5 Measurement commands

Table  8  and  9  show  the  measurement  commands  of  the  Hera.  The
MEASure  commands  measure  the  requested  values  using  the  set
averaging and integration time and returns the result in ASCII format. The
SAMPle  commands  measure  the  requested  parameters  using  a  sample
count and delay time and return an array of data. The array contains single
float array of data.

Command syntax Parameters

Range

Purpose

:MEASure:XYZ

None

Measure XYZ

:MEASure:Yxy

None

Measure Y and x,y
colour point

:MEASure:Yuv

None

Measure Y and u',v'
colour point

:MEASure:
SPECtrum

None

Measure the spectrum
The output is in the
selected resolution
and either uses factory
calibration or user
calibration

:MEASure:
RAWSPECtrum

None

Measures the raw
spectrum, suitable for
user calibration

:MEASure:TEMP

None

Measures the sensor
temperature

:GET:WAVE
lengths

Pixels

Get the wavelength
axis according to the
set resolution

:SAMPle:
SPECtrum

Samples

– 500

Performs High speed
sampling of a
spectrum

:SAMPle:
SPECtrum:READ

Index

– 500

Reads the sampled
spectrum at index.

Table 8 Measurement commands.

Special
measurement
commands

Parameters

Range

Purpose

:MEASure:CRI

Number of
test samples

8 or 15

Measure the CRI of a
light source, see
comment

:MEASure:
PEAKWL

None

Measures the peak
wavelength

:MEASure:DWL

None

Measures the
Dominant wavelength
and purity

:MEASure:ALL

CRI

0/1

Measures all
parameters with or
without CRI

:MEASure:
LEDCHAR

CRI

0/1

Measures all
parameters with or
without CRI

:MEASure:CCT

None

Measures the
correlated color
temperature

Table 9 Measurement commands.

Note: CRI calculation takes about 11ms additional time to measure a spectrum. Using the
Admesy colour DLL, this can be achieved faster.

5.6 User EEPROM commands

Table  10  shows  the  commands  which  can  be  used  to  store  values  in  the
user  EEPROM  space.  It  is  advised  to  reboot  the  Hera  after  writing  new
values to the EEPROM.

Command syntax Parameters

Range

Purpose

:EEPROM:
STARTUP:READ

None

Copies start up
conditions from
EEPROM to internal
variables.
Values can then be
read using
:SENSe:AVERage? for
example

:EEPROM:
STARTUP:WRITE

None

Copies internal
variables to EEPROM

:EEPROM:
CONFigure:MODE

Mode

0 = USB
1 = Ethernet
2 = RS232

Configures the mode

:EEPROM:
CONFigure:
MODE?

None

Reads the mode at set
in the EEPROM

:EEPROM:
CONFigure:
BAUDRATE

Baudrate

0 = 9600
1 = 19200
2 = 38400
3 = 57600
4 = 115200
5 = 230400

Configures the RS232
baudrate in the
EEPROM

:EEPROM:
CONFigure:
BAUDRATE?

None

Read the current
RS232 baudrate from
EEPROM

:EEPROM:
CONFigure:TRIG

Trigger

0 = off
1 = on

Configures triggering

:EEPROM:
CONFigure:TRIG?

None

Reads from EEPROM
if triggering is used.

:EEPROM:
CONFigure:TRIG
DELAY

Delay

0 - 30000000

Configures a delay
before triggering in
microseconds

:EEPROM:
CONFigure:TRIG
DELAY?

None

Reads the configured
delay before triggering

:EEPROM:
CONFigure:IP

IP address

Example:

192.168.0.100

Configures the
Ethernet IP address

:EEPROM:
CONFigure:IP?

None

Reads the current IP
address from
EEPROM

:EEPROM:
CONFigure:GW

Gateway

Example:
192.168.0.1

Configures the
Ethernet gateway

:EEPROM:
CONFigure:GW?

None

Reads the current
gateway address from
EEPROM

:EEPROM:
CONFigure:MASK

Ethernet
mask

Example:
255.255.255.
0

Configures the
Ethernet mask

:EEPROM:
CONFigure:MASK
?

None

Reads the current
ethernet mask from
EEPROM

:EEPROM:
CONFigure:RES

Resolution

0 = 0.5nm
1 = 1nm
2 = 2.5nm
3 = 5nm
4 = 10nm

Configures the
resolution in EEPROM

:EEPROM:
CONFigure:RES?

None

Reads the resolution
from EEPROM

:EEPROM:
CONFigure:SPINT

Int time

1000

–

500000

Configures default
spectrometer
integration time

:EEPROM:
CONFigure:
SPINT?

None

Reads the default
spectrometer
integration time from
EEPROM

:EEPROM:
CONFigure:
SPAVG

Averaging

– 4000

Configures default
spectrum averaging

Command syntax Parameters

Range

Purpose

:EEPROM:
CONFigure:
SPAVG?

None

Reads the default
spectrum averaging
from EEPROM

:EEPROM:
CONFigure:
AUTORANGE

Auto-range

0 = off
1 = on

Configures
autoranging

:EEPROM:
CONFigure:
AUTORANGE?

None

Reads the current
auto-range setting from
EEPROM

:EEPROM:
CONFigure:
INTERPOL

Interpolation

0 = linear
1 = cosine
2 = cubic
3 = Catmull-
Rom
4 = Hermite

Configures the
interpolation method to
be used

:EEPROM:
CONFigure:
INTERPOL?

None

Reads the current
interpolation method
from EEPROM

:EEPROM:
CONFigure:
SPSBW

Calibration
matrix

“off” or “user”

Configures the default
spectrometer
calibration matrix to be
used

:EEPROM:
CONFigure:
SPSBW?

None

Reads the default
spectrometer
calibration matrix from
EEPROM

:EEPROM:
SPSBW:WRITE

Row,
Column
Value

– 2

single float

Writes the values of
the spectrum matrix to
Hera

:EEPROM:
SPSBW:READ

Row
Column

– 2

Reads the values of
the spectrum matrix
from Hera

:EEPROM:READ:
USERCAL

None

Reads the user
calibration values
from EEPROM to
memory

Command syntax Parameters

Range

Purpose

:EEPROM:WRITE:
USERCAL

None

Write the user
calibration values form
memory to EEPROM.
This step fixes all
values for a next
restart of the
instrument

:EEPROM:
READ:ID

None

Reads the device ID. This is
useful for use with Medusa or
any other system with multiple
units attached. The deviceID
can be used to link to a
mechanical position of the
instrument, which can then be
selected by software for a
specific task

:EEPROM:WRITE:
ID

ID number

– 255

Write the device ID to
EEPROM

:EEPROM:ABS:
WRITE

Index,
Parameter,
value

Write the user absolute
spectrum parameters

:EEPROM:ABS:
READ

Index,
parameter

Reads the user
absolute spectrum
parameters

:EEPROM:ABS:
FIX

None

Fixes the user absolute
spectrum parameters
in the EEPROM

:EEPROM:
CONFigure:
WHITE

White point

“D65”, “A”,
etc

Used for Dominant
wavelength

:EEPROM:
CONFigure:
WHITE?

None

Gets the currently
configured white point

:EEPROM:
READ:UNIT

None

0 Radiant
power
1 Radiance
2 Irradiance
3 Radiant
intensity

Reads the calibrated
unit as set from factory

Command syntax Parameters

Range

Purpose

:EEPROM:CONFi
gure:AUTO:FREQ

Frequency
(Hz)

– 255

Auto-range parameter:
frame frequency of the
source (display) to
measured

:EEPROM:CONFi
gure:AUTO:
FREQ?

None

Reads the set
frequency

:EEPROM:CONFi
gure:AUTO:
ADJMIN

Adjmin (%)

– 100

Auto-range parameter:
The minimum level to
adjust to

:EEPROM:CONFi
gure:AUTO:
ADJMIN?

None

Reads the set Adjmin
for the spectrometer

:EEPROM:CONFi
gure:MAXINT

Max int

1000

–

1000000

Maximum
spectrometer
integration time. If time
is too short, measuring
dark level may be
difficult

:EEPROM:CONFi
gure:MAXINT?

None

Query the maximum
spectrometer
integration time

:EEPROM:
CONFigure:
USERABS

Absolute
calibration

0 = factory
1 = user

Configures the
absolute calibration
mode to be used.

:EEPROM:
CONFigure:
USERABS?

None

Reads the absolute
calibration mode from
EEPROM

:EEPROM:READ:
SBWNAME

Matrix
number

Reads the name of an
XYZ matrix

:EEPROM:
READ:SN

None

Read serial number

Table 10 User EEPROM commands.

5.7 Returned results

:MEASure command return their result in ASCII formatted floating point as
shown below.

(X,Y,Z,clip,noise) → %f,%f,%f,%d,%d

X,Y,Z can be substituted for Y,u,v or other colour spaces. :SAMPle
command return all measurement data also in ASCII format., except the
:Sample:Y function. The first three values indicate the delta time between
samples and the clip and noise values.

MEAS command

%f\n

Clip

%f\n

Noise

%f\n

Value1

%f\n

Value2

%f\n

Value3

%f\n

Table 11 Return result MEAS command.

Exceptions to the above is the :MEASure:TEMP command which only
gives back the temperature.

6 Measurement example

The Hera uses  default settings  when  the device  is started. These can be
programmed  by  the  end  user  so  that  the  device  starts  with  the  same
settings each time it is connected.

Although  it's  possible  to  program  all  Hera  devices  in  production
environment  to  start  with  equal  settings,  it  is  recommended  to  set  the
averaging,  integration  time  and  SBW  values  in  the  initialization  routine  of
the host software.

A typical measurement example of XYZ would include the following
commands as shown on the right.

Fig 4 Measurement example.

Action may be performed in a loop

Open device (VISA open, RS232 port init)

Set averaging to 1 sample

Set integration time to 16.666ms

Set calibration matrix to the first user
programmable matrix

Set auto-ranging on

Measures CIE X, Y and Z

Read the result back from device
(VISA/USBTMC read command or RS232 read)

open device

close device

:sens:aver 1

:sens:int 16666

:sens:sbw user1

:sens:autorange 1

:meas:xyz

read result

Close the device

7 Autoranging

7.1 Introduction

The  Hera  includes  an  auto  range  function  for  the  spectrometer  sensor.
This  function  is  useful  in  case  the  measured  object  shows  an  unknown
luminance value. In this case, the Hera will try to find the optimum setting
which is a trade-off between speed and the stability of the instrument. The
autoranging function can also be fine-tuned to reach better stability levels
by  setting  a  few  parameters.  Autoranging  can  be  controlled  by  3
parameters.



Frequency : supposed to be frame frequency of the source
(display) that is measured



Adjmin : The minimum level to adjust to

Adjmin can vary between 1 and 100. Reasonable results will be achieved
when set to 40 for the spectrometer regarding the speed and the stability.
If  high  stability  is  needed,  this  setting  must  be  increased  (but
measurements  will  become  slower).  If  a  faster  measurement  is  needed
and  the  stability  level  may  be  lowered  a  little, the  value  of  adjmin  can  be
decreased. When  the  Hera measures  in  auto  range  mode, it  can  happen
that  the  found  integration  time  is  very  low.  For  example  when  measuring
white  it  may  be  just  7ms. When  this  happens,  the  Hera  will  automatically
increase  the  averaging  so  that  the  total  measurement  time  equals  >=
(1/frequency)

averaging.

7.2 How autoranging works

The  auto  ranging  works,  by  first  setting  a  default  integration  time.  If  this
already meets the criteria for a good measurement, the measurement will
be  done  using  that  integration  time.  It  should  be  clear  that  this  is  the
fastest because no adjustment will be done. In case the measured result is
either  to  low  or  too  high  (clip),  than  the  Hera  will  adjust  to  a  better  level.
The following graph shows how levels inside the Hera work.

Fig 5 Autorange levels

When auto-

ranging is set, the Hera will accept any level between “Adjmin”

and “Adjmax” as a good signal. The Adjmin level can be set by the user
through a software command, allowing some fine tuning of the stability and
the speed of the instrument.

adjmin level

adjmax level

clipping

7.3 Auto-range parameters

Auto-range controls the following parameters:



Frequency:

This setting must be set to the frame frequency of the

measured sample. The range is 1 to 255 Hz.



Adjmin:

The adjmin parameter is very important. The higher this

level is set, the more stable the measurement becomes, but it also
slows down the measurement if set too high. That means, there is
a trade-off between speed and stability. It mainly affects the lower
grey scale levels. If these levels appear not stable, adjmin needs
to be increased. Adjmin is set from 1-100, which means 1-100% of
the Adjmax level (Adjmax is fixed by Admesy).



Maximum integration time:

Although not really part of the auto-

ranging  algorithm,  this  parameter  is  used  when  the  auto-ranging
result  exceeds  this  setting  of  integration  time.  When  the  grey
scales  are  low  (grey  scale  0  for  example),  the  maximum
integration  time  setting  can  be  used  to  allow  only  a  maximum
measurement  time.  Of  course  this  affects  stability  (longer
measurement is always more stable), but again this  is a trade-off
for production environments to save on test time.



Averaging:

The averaging will only be used if the auto-range

algorithm does calculate a averaging that is less than the set
averaging for the spectrometer sensor.

7.4 Auto-range in practice

When auto-ranging is set, the measurement settings (integration time, gain
and averaging) are automatically adjusted. An initial measurement is done
to determine the final settings of averaging and integration time, based on
the settings of frequency and adjmin.

The  set  integration  time  (1/frequency  as  set  in  the  EEprom  auto-range
frequency  parameter)  of  the  instrument  will  always  be  used  as  the  first
value  to try.  If  this  setting  results  in  a  value  between  adjmin  and  adjmax,
no further actions are necessary and the speed is optimal.

When  measuring  a  display  we  can  measure  random  patterns,  but  mostly
known  patterns  are  measured.  Setting  an  integration  time  that  is  nearly
right, 1/frequency (Hz) is preferred, as it optimizes the speed for adjusting
the auto ranging settings and thus provides optimal results.

Example: a 23” TFT display (standard desktop LCD) with white at
290 cd/m² and a frame rate of 60Hz. Settings for auto ranging are:



Frequency = 60



Adjmin SP = 40



Max int SP = 3000000

These settings will provide a stable measurement on white and black.
Auto-range algorithm will adjust to measure black 0.3cm/m

with 3000ms

integration time, resulting in ~5600ms tact time for the spectrometer
sensor.

7.5 Programming Hera for auto-ranging

The  Hera  has  start-up  settings.  This  means  that  when  the  Hera  is
connected  to  a  PC  or  pattern  generator,  it  only  needs  the  “:meas:Yxy”
command  to  get  luminance  and  colour  data.  All  other  settings  can  be
saved as preset and are loaded when the instrument is started. However,
it requires the right settings to be set in advance. This can be done though
the  Admesy  Iliad  application  and  select  Device



Start-up settings



Hera.

These setting may be optimized per display type. There are a few
categories we can define. Those are shown in the next chapters.



Display without PWM:

This can be measured using almost any

settings,  but  the  settings  may  be  optimized  for  high  speed.  This
means,  we  can  use  a  short  integration  time  for  bright  images
(white  for  example)  and  decreased  the  maximum  integration  of
black  to  a  level  that  gives  stable  results  and  is  still  fast.  In  this
case the frequency setting is not critical.



Display with PWM:

Since the luminance will show PWM, a

measurement must at least cover 1 full frame. Taking more frames
will result in better stability. In this case the frequency setting is
apparently more critical to get a good stability.

7.6 Auto-ranging recommendations

It is recommended to apply auto ranging in case process variation is high
or in case various grey scales are measured. In cases where luminance
setting is known, it may be desirable to turn off auto-ranging to save
additional measurement / test time.

Regarding the grey scales, like a gamma measurement is performed,
speeds up the measurement significantly, when using auto-ranging in
combination with the feedback function.

There are a lot of ways to fine tune the Hera for each application. Take this
document  into  consideration  and  apply  the  comments  correctly.  By
assuming  that  any  default  setting  will  do,  it  will  lead  to  a  non-optimal
measurement  results.  Any  measurement  is  application  dependent.  One
should  consider  that  auto-range  settings  exist  for  the  sole  purpose  of
optimizing each application.

8 Hera measurement results

The Hera is a spectrometer that provides direct calibrated output. As from
many other mini spectrometers the Hera differs in great processing power.
Spectrum conversion to XYZ is done inside the Hera and so are all colour
space  conversions,  including  CRI  calculation.  Apart  from  this  internal
calculation,  it  is  also  possible  to  receive  the  spectral  data  and  do    the
processing  on  the  host  PC.  This  can  be  done  by  Admesy’s  colour  DLL.
The  calculations  performed  inside  the  Hera  are  based  on  the  same
f

ormula’s as the DLL. Calculations done inside Hera are performed using

single precision floats and the DLL uses double precision.

For formula’s

please check the user manual of the Admesy colour DLL.

9 Operating modes & triggering

The operating mode only matters in trigger mode. The mode is used to
send back results by USB, Ethernet or RS232. The modes of the Hera are:



USB mode



Ethernet mode



RS232 mode

A trigger actives only one command,

for example “:meas:xyz”. This

command needs to be set first by the host. After a trigger is received, the
command will execute and the result will be presented on the selected
interface as shown above. The Hera responds to a rising edge of the
trigger signal.

Admesy B.V.
Sleestraat 3
6014 CA Ittervoort
The Netherlands

T +31 (0)475 600 232
F +31 (0)475 600 316

www.admesy.com
info@admesy.com

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Version 1.0.10 08/2017