Barometer/Humidity Sensor

Table of Contents:

Introduction

A Vaisala PTU-300 is used to monitor variations in room temperature, relative humidity (RH) and atmospheric pressure. This data will be recorded as instrument telemetry and monitored to ensure there is no correlation between instrumental shifts (spectral movement) and atmospheric pressure or room temperature changes.

Given the main spectrometer is within a vacuum chamber, the RH of the surrounding room air does not impact instrumental stability. However, extremely low RH values can affect the lifetime of electronic devices, and hence this parameter is monitored and recorded within instrument telemetry.

The Vaisala PTU300 is mounted on the wall of the thermal enclosure. A hose connected to the pressure-measuring spigot on the PTU300 goes through the wall to measure the pressure inside the spectrometer thermal enclosure. This allows pressure within the thermal enclosure to be measured while placing the the heat source of the Vaisala itself outside in the hallway.

Relevant Devices

Description	Qty	Source	Part Number	Notes
Barometer/Humidity Sensor	1	Vaisala	PTU300	Note Vaisala now offers an ethernet interface board for the PTU300, but it has to be installed at the factory.
Serial Interface Cable	1	Vaisala	19446ZZ	Purchased separately and installed by KPF team.
RS-232 to Ethernet Adapter	1	Lantronix	UDS2100	This is the version with two serial ports (but standard 9-pin RS-232 connectors)

Relevant Functional Block Diagram

Software Actions

	Action	Notes
1	Read pressure value	Value reported as telemetry (see below)
2	Read temperature value	Value reported as telemetry (see below)
3	Read relative humidity value	Value reported as telemetry (see below)

Required Adjustable Settings

Setting	When Needed			Notes
	Build	Observing	Maintenance
Pressure measurement frequency	Yes	No	Maybe	Set in configuration file. If this needs to be changed, edit configuration file, re-install, and then restart dispatcher.
Temperature measurement frequency	Yes	No	Maybe	See pressure.
Relative humidity measurement frequency	Yes	No	Maybe	See pressure.

Required Telemetry

	Parameter	Report Frequency	Purpose	Notes
1	Pressure measurement	Once every 5 sec	Environmental monitoring	Managed through configuration file
2	Temperature measurement	Once every 5 sec	Environmental monitoring	See pressure.
3	Relative humidity measurement	Once every 5 sec	Environmental monitoring	See pressure.

Required Alarms

The Alarms page collects alarms across the entire KPF system.

A direct link to the Vaisala section of the Alarms page is given here.

Relevant Datasheets & Manuals

	Description	Source
1	Vaisala PTU300 User’s Guide (2019 version; device purchased in 2014)	https://www.vaisala.com/en/products/instruments-sensors-and-other-measurement-devices/instruments-industrial-measurements/ptu300
2	Calibration Certificates	These shipped with our actual KPF device
3	Lantronix UDS 2100 Quick Start Guide	https://www.lantronix.com/products/uds2100/#tab-docs-downloads
4	Lantronix UDS 2100 User Guide	https://www.lantronix.com/products/uds2100/#tab-docs-downlo

Relevant Software

Description

Files

1

Python 2 software written by a student some years back. These lines of code were used to read values from the Vaisala while it was installed at Keck.

That installation was using a USB interface on a Windows machine. Not sure if the current serial interface will change anything here.

2

As part of the KROOT distribution, there is a SerialStream interface which manages connections to and from serial hosts. This includes managing Lantronix connections.

Dispatcher Implementation

Keyword	Value	Type
RETVAL	Value returned by Vaisala.	String. The format is set in the configuration file. Only readable.
TIME	Time stamp of when the last RETVAL was received.	Unix timestamp (binary) or time stamp (ascii). Only readable.
PRES	Pressure value in units of hPa.	Double value from RETVAL, read only.
RELH	Relative humidity in %.	Double value from RETVAL, read only.
TEMP	Temperature in deg C.	Double value from RETVAL, read only.
DISP#STA	Dispatcher status.	Enum and read only. If value is 4 or “Not Connected” the connection to the Vaisala or the Lantonix is not available. If value is 3 or “Connecting” the dispatcher is attempting to connect to the Vaisala through the Lantronix.
DISP#CONN	IP address and port separated by a colon.	Read only string, set by configuration file
DISP#DEV	Device name	Read only string, set by configuration file

Dispatcher Configuration File

Configuration	Value	Explanation
ip	192.168.23.126	IP address of the Lantronix box.
port	10001	Port that is used for Vaisala, this is port 1.
format_str	form 9.4 "P=" P " " U6 6.4 "T=" T " " U3 6.4 "RH=" RH " " U4 \r \n	Format statement of the output from the Vaisala. At dispatcher start up and at every new connection, this value is sent to the Vaisala. The #.# sets the number of characters (first # ) and the second # sets the number of characters after the decimal point. There must be a space between the characters that notes what the value is (such as P=) and the actual value (the P). The code uses the characters (P=, RH= or T=) to determine what the next value is.
poll_time	5	Time between reads of the Vaisala in seconds.