Table of Contents:
Introduction
A device that allows a large number of temperature sensors to be daisy-chained along a main branch cable. We are using these sensors throughout the system for temperature measurements that do not require the precision/accuracy/expense of a Lakeshore controller.
Relevant Devices
Description | Qty | Source | Part Number | Link |
|---|---|---|---|---|
Sensor Controller | 1 | iButtonLink | LinkHub-E 32K | |
Power Supplies | 1 | iButtonLink | HubPwr5-NA | |
Sensors | TBC (Likely a couple dozen of them) | Maxim Integrated | DALLAS 18B20 1441C4 +800AB (label on devices used on ICON) | https://www.maximintegrated.com/en/products/sensors/DS18B20.html |
Photos of Device
The sensors are semiconductor devices with three pins:
The sensor cables connect to the base via a custom cable, with an RJ-45 (ethernet) connector on one end and the sensors on the other. The base unit allows four sensor cables to be attached to it (with multiple sensors on each cable, like the one shown here).
For the cable shown here a Winchester connector was used to allow the sensor section to be easily separated from the ethernet cable section. We will likely employ the same scheme for KPF.
Note how the sensors can branch off the ‘main line', and also branch off the ‘branches’.
Relevant Functional Block Diagram
Note while we will have separate cables, the python code below does not differentiate by cable when it combines sensor IDs into a list.
Software Actions
Action | Notes | |
|---|---|---|
| 1 | Read temperature values from all sensors | |
| 2 | ||
| 3 |
Required Adjustable Settings
Setting | When Needed | Notes | ||
|---|---|---|---|---|
Build | Observing | Maintenance | ||
Sensor location table(s) | YES | NO | MAYBE | |
Sensor Read Frequency | YES | NO | MAYBE | |
Device Setup Parameters
The current device settings can be listed through a telnet connection (see instructions below for changing IP address).
The current list of settings is included in the file here. Note our device was used previously by another project, so while these are the current settings they may not be the default settings.
Note the listing is provided here for reference only; we do not need to query or set these parameters in software.
Required Telemetry
Parameter | Report Frequency | Purpose | Notes | |
|---|---|---|---|---|
| 1 | Temperature of each thermal sensor | Once per minute TBC (Set by Sensor Read Frequency value) | Monitor temperatures | |
| 2 |
Sensor Name Look-up Tables
Each sensor has a unique ID that is used by the LinkHub-E base. The IDs are not easily remembered so we’ll want a look-up table to tie the sensor IDs to a KPF sensor location.
KPF Long Name | KPF Short Name | Sensor ID | Notes | |
|---|---|---|---|---|
| 1 | e.g. Exposure Meter Enclosure | e.g. 2890F1DD06000089 | ||
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Required Alarms
Parameter | Threshold | Notes | |
|---|---|---|---|
| 1 | Temperature too high | TBC | |
| 2 | Temperature too low (TBC) | TBC |
Relevant Datasheets & Manuals
Description | File | Source | |
|---|---|---|---|
| 1 | LinkHubE User Guide | ||
| 2 | LINK Family Manual | https://cdn.shopify.com/s/files/1/0164/3524/files/The_LINK_Family_Manual_1.7.pdf?7145028656254187831 | |
| 3 | Command Reference | ||
| 4 | Sensor Datasheet Sensor was originally developed by Dallas Semiconductor but they are now owned by Maxim Integrated |
Relevant Software
Description | File | Source |
|---|---|---|
LinkHub_E_python.py is the main program. LinkHub_E_commands.py contains functions called by the main program. This code finds all of the sensors connected to the LinkHub E, and then reads their values. Note first reading might report all temperatures as ‘85’; this seems to be a consequence of the first read to find sensor IDs. The sensor IDs and values are read into a list format. Note this software does not differentiate between the 4 possible cables connected to the base unit; all sensors from all cables are added together into the same list. | Python code originally written by Y. Ishikawa (SSL). Simplified by S. Gibson to remove sections not relevant to KPF. |
Installation Instructions
Description | File |
|---|---|
Instructions on how to change the device’s IP address over Telnet |
Dispatcher Implementation
This dispatcher is part of kpfmet (currently.)
There are an arbitrary number of sensors for the unit. The names, denoted as $(NAME), are stored in the configuration file, as are the ID or address values. Readout is done in serial for the device, and done in the order of appearance in the configuration file. The “#” denotes the dispatcher number. Currently that is 4 for the kpfmet service but if dispatcher is moved or the service rearranged, this could change.
Keyword | Value | Type |
|---|---|---|
$(NAME) | Temperature in deg C | Double - read only |
$(NAME)_ID | ID value | String - read only |
LINKSTA | 0 - Done 1 - Reading When Reading, the temperature values are being retrieved and the values will appear in the keywords. Reading values is slow, so this update only reads 10 values at a time, looping through so that each value is eventually read. | Enumerated - read only |
MODEL# | Model of the hub, value of the command ' '. | String - read only |
DISP#CLK | Number of whole seconds dispatcher has been alive | Integer - read only |
DISP#ERR | Error value | Integer - read only |
DISP#MSG | Message from the dispatcher | String - read only |
DISP#REQ | Last keyword requested to be modified, written before modify is sent. | String - read only |
DISP#MEM | Memory used by dispatcher in kB | Integer - read only |
DISP#STA | Status of the dispatcher 0 - Ready - working 1 - Initializing - only true during start up 2 - Shutting down - A control-C or the stop command has been issued 3 - Connecting - Attempting to connect to the device 4 - Not Connected - No connection to the device | Enumerated - read only |
DISP#STOP | Stop command which ends the dispatcher. 0 - Continue 1 - Stop | Enumerated |
DISP#CONN | IP address and port number separated by a colon. | String - read only |
DISP#DEV | Device name | String - read only |
Configuration File
The required sections are:
device which has the first four configuration keyword value pairs
dispatcher which has the dispnum value
[0], [1], [2], … [number-1] - A section for each sensor, starting from 0, and the total number must match the value of the number configuration. Extra sections are ok, but if any are missing the dispatcher will throw an error message and exit.
Configuration | Value | Explanation |
|---|---|---|
ip_address | 192.168.23.184 | IP address of device |
port | 10001 | Port for telnet connection to device |
number | 31 | The number of active sensors |
poll_time | 20 | The time between requests for temperature measurements |
dispnum | 4 | Number of the dispatcher in the service |
name | temp0 | The human readable name requested for a temperature value, will set the keyword name |
id | 2890F1DD06000089 | The ID value for the temperature measuring device on the hub. This is what will be referenced. Note- This is the reverse of the order that the ID number is returned when querying the device. There is a swap of byte order and this is the ID that must be used for a lookup |
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