MKS 905 MicroPirani Guide

905 MicroPiraniTM Sensor Kit
RS232 / RS485
Design Guide
P/N: 100013905
Revision: A, September, 2007

Extent of the Warranty
MKS Instruments, Inc., HPS™Products Inc. and MKS Denmark ApS warrants the 905-00XX MicroPirani™ Sensor Kit and its accessories to be free from
defects in materials and workmanship for one (1) year from the date of shipment by HPS™or authorized representative to the original purchaser
(PURCHASER). Any product or parts of the product repaired or replaced by HPS™under this warranty are warranted only for the remaining unexpired part
of its one (1) year original warranty period. After expiration of the applicable warranty period, the PURCHASER shall be charged HPS™’ current prices for
parts and labor, plus any transportation for any repairs or replacement.
ALL EXPRESS AND IMPLIED WARRANTIES, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE, ARE LIMITED TO THE WARRANTY PERIOD. NO WARRANTIES, EXPRESS OR IMPLIED, WILL APPLY AFTER THIS PERIOD.
Warranty Service
The obligations of HPS™under this warranty shall be at its option: (1) to repair, replace, or adjust the product so that it meets applicable product
specifications published by HPS™or (2) to refund the purchase price.
What Is Not Covered
The product is subject to above terms only if located in the country of the seller from whom the product was purchased. The above warranties do not apply
to:
I. Damages or malfunctions due to failure to provide reasonable and necessary maintenance in accordance with HPS™operating instructions.
II. Damages or malfunctions due to chemical or electrolytic influences or use of the product in working environments outside the specification.
III. Fuses and all expendable items which by their nature or limited lifetime may not function for a year. If such items fail to give reasonable service for a
reasonable period of time within the warranty period of the product; they will, at the option of HPS™, be repaired or replaced.
IV. Defects or damages caused by modifications and repairs effected by the original PURCHASER or third parties not authorized in the manual.
Condition of Returned Products
HPSTM will not accept for repair, replacement, or credit any product which is asserted to be defective by the PURCHASER, or any product for which paid or
unpaid service is desired, if the product is contaminated with potentially corrosive, reactive, harmful, or radioactive materials, gases, or chemicals.
When products are used with toxic chemicals, or in an atmosphere that is dangerous to the health of humans, or is environmentally unsafe, it is the
responsibility of the PURCHASER to have the product cleaned by an independent agency skilled and approved in the handling and cleaning of
contaminated materials before the product will be accepted by HPSTM for repair and/or replacement.
In the course of implementing this policy, HPSTM Customer Service Personnel may inquire of the PURCHASER whether the product has been contaminated
with or exposed to potentially corrosive, reactive, harmful, or radioactive materials, gases, or chemicals when the PURCHASER requests a return
authorization. Notwithstanding such inquiries, it is the responsibility of the PURCHASER to ensure that no products are returned to HPS™which have been
contaminated in the aforementioned manner.
Other Rights and Remedies
I. These remedies are exclusive. HPS™SHALL NOT BE LIABLE FOR CONSEQUENTIAL DAMAGES, FOR ANTICIPATED OR LOST PROFITS,
INCIDENTAL DAMAGES OR LOSS OF TIME, OR OTHER LOSSES INCURRED BY THE PURCHASER OR BY ANY THIRD PARTY IN CONNECTION
WITH THE PRODUCT COVERED BY THIS WARRANTY, OR OTHERWISE. Some states do not allow exclusion or limitation of incidental or consequential
damage or do not allow the limitation on how long an implied warranty lasts. If such laws apply, the limitations or exclusions expressed herein may not
apply to PURCHASER.
II. Unless otherwise explicitly agreed in writing, it is understood that these are the only written warranties given by HPS™. Any statements made by any
persons, including representatives of HPS™, which are inconsistent or in conflict with the terms of the warranty shall not be binding on HPSTM unless
reduced to writing and approved by an authorized officer of HPS™.
III. This warranty gives PURCHASER specific legal rights, and PURCHASER may also have other rights which vary from state to state.
IV. For HPS™products sold outside of the U.S., contact your MKS representative for warranty information and service.
Warranty Performance
To obtain warranty satisfaction, contact the following:
US & ASIA:
MKS Instruments, Inc., HPS™Products, Inc., 5330 Sterling Drive, Boulder, CO 80301, USA, Phone: [phone].
EUROPE:
MKS Denmark ApS, Ndr. Strandvej 119G, DK3150 Hellebaek, Denmark, Phone: [phone], Email: mksdenm[email protected]
Part number: 905-00 _ _
Serial number: _ _ _ _ _ _ _ _ _ _
Please fill in this number and have it readily available when calling for service or additional information.
The part number can be found on your packing slip, and both the part number and serial number are
located on the electronics module.
© 2007 MKS Instruments. All rights reserved.
Trademarks used in this manual: MicroPirani™ are a trademark of MKS Instruments Inc. Windows®is a trademark of Microsoft
Corporation

Table of contents
Symbols used in this manual............................................................................................................................. 1
Package contents.............................................................................................................................................. 2
About the 905 MicroPirani™ Sensor Kit............................................................................................................ 3
905 MicroPirani™ Sensor Kit specifications ................................................................................................. 5
MicroPirani™ electronics module pinout....................................................................................................... 5
Electronics module dimensions..................................................................................................................... 6
MicroPirani™ sensor and board dimensions ................................................................................................ 6
About the evaluation board................................................................................................................................ 7
Evaluation board overview............................................................................................................................ 8
Connections.............................................................................................................................................. 8
D-SUB male connector pinout .................................................................................................................. 8
Specifications............................................................................................................................................ 8
Getting started with the 905 MicroPirani™ Sensor Kit...................................................................................... 9
Installing the electronics module............................................................................................................... 9
Connecting the electronics module with the sensor ................................................................................. 9
Choosing communication standard .......................................................................................................... 9
Connecting the communication cable....................................................................................................... 9
Powering up the system.......................................................................................................................... 10
Analog output.......................................................................................................................................... 10
Integrating the 905 MicroPirani™ Sensor Kit .................................................................................................. 11
Choosing a power supply............................................................................................................................ 11
MicroPirani™ electrical connections ........................................................................................................... 12
Flexible flat cable .................................................................................................................................... 12
Regular cable.......................................................................................................................................... 13
Printed circuit board connection.............................................................................................................. 13
Installing the MicroPirani™ sensor.............................................................................................................. 13
Communication ........................................................................................................................................... 14
Example configuration for RS232 and RS485........................................................................................ 14
The signal ‘RS485_ENABLE’.................................................................................................................. 14
Analog Output ............................................................................................................................................. 15
Pressure to voltage table........................................................................................................................ 16
Utilization of remote zero............................................................................................................................. 16
Ground to earth connection......................................................................................................................... 17
Reset switch................................................................................................................................................ 17
Activity LED................................................................................................................................................. 18
Set point outputs ......................................................................................................................................... 18
Integrating the electronics module onto a printed circuit board .................................................................. 18
Updating the firmware................................................................................................................................. 19
Manual procedures for the 905........................................................................................................................ 20
Adjustment for Zero..................................................................................................................................... 20
Venting to Atmosphere................................................................................................................................ 20
Leak Detection ............................................................................................................................................ 20
Operation......................................................................................................................................................... 21
MicroPirani™ Sensor Kit factory defaults table........................................................................................... 21
RS-485 Protocol.......................................................................................................................................... 22
Standard Addresses ............................................................................................................................... 22
Universal Addresses............................................................................................................................... 22
Query and Command Syntax.................................................................................................................. 22
Response Syntax (ACK/NAK)................................................................................................................. 22
RS232 / RS485 Command Set........................................................................................................................ 23
Set Up Commands...................................................................................................................................... 23
Address – AD.......................................................................................................................................... 23
Baud Rate – BR...................................................................................................................................... 23
Factory Default – FD............................................................................................................................... 23
RS Delay – RSD ..................................................................................................................................... 24
Test RS485 – TST .................................................................................................................................. 24
Unit – U................................................................................................................................................... 24
User Tag – UT......................................................................................................................................... 24
Status Commands....................................................................................................................................... 25
Device Type – DT................................................................................................................................... 25
Firmware Version – FV........................................................................................................................... 25
Hardware Version – HV.......................................................................................................................... 25

Manufacturer – MF.................................................................................................................................. 25
Model – MD............................................................................................................................................. 25
Pressure Reading – PR1........................................................................................................................ 25
Serial Number – SN................................................................................................................................ 25
Time On – TIM........................................................................................................................................ 26
Transducer Temperature – TEM............................................................................................................. 26
Set Point Commands .................................................................................................................................. 26
Set Value – SP1,SP2,SP3...................................................................................................................... 27
Hysteresis Value – SH1, SH2, SH3........................................................................................................ 27
Set Point Direction – SD1, SD2, SD3..................................................................................................... 28
Enable Set Point – EN1, EN2, EN3........................................................................................................ 28
Set Point Status – SS1, SS2, SS3.......................................................................................................... 28
Calibration and Adjustment Commands...................................................................................................... 29
Atmospheric Calibration – ATM.............................................................................................................. 29
Gas Type Calibration – GT..................................................................................................................... 29
Vacuum adjustment – VAC..................................................................................................................... 29
How the MicroPirani™ Sensor Works............................................................................................................. 30
Ordering information........................................................................................................................................ 31
For more information contact:
MKS Denmark ApS
Ndr. Strandvej 119G
DK-3150 Hellebæk
Denmark
Tel: [phone] – Fax: [phone]
Email: [e-mail]
MKS Instruments, HPS Products
5330 Sterling Dr.
CO-80301 Boulder
USA
Tel: [phone] - Fax: [phone]

Series 905 Page 1 Design Guide
Symbols used in this manual
Failure to read message could result in damage to the equipment
)
Calls attention to important procedures, practices or conditions.

Series 905 Page 2 Design Guide
Package contents
Before unpacking the 905 MicroPirani™ Sensor Kit, check all surfaces of the packaging material for
shipping damage. Please make sure that your package contains the following items with respect to the last
four digits of the part number:
Partnumber TO-5 Sensor
board Sensor cable Flange Electronics module Evaluation board Power supply Short doc. Design guide
905-0001 1 1 1 KF16 1 1 - 1 1
905-0002 1 1 1 KF16 1 1 1 1 1
905-0003 1 - - - 1 - - 1 -
905-0004 1 1 1 - 1 - - 1 -
If any items are missing, please call MKS Customer Service at [phone] or [phone] or your
local MKS sales office or distributor. Inspect for visible damage. If found, notify the carrier immediately.
Use caution when unpacking the 905 MicroPirani™ Sensor Kit and note the following:
The TO-5 sensor is very delicate and should never be touched on its surface, as this will
damage the bonding wires and/or sensor element.
The electronics module and evaluation board are sensitive to static electricity. Observe all ESD
safety precautions while handling these parts. Failure to follow ESD safety precautions could
result in damage to the electronics.

Series 905 Page 3 Design Guide
About the 905 MicroPirani™ Sensor Kit
The 905 MicroPirani™ Sensor Kit is an ultra
compact wide range vacuum pressure transducer
designed for OEM system integration. The transducer
is based on well proven thermal conductivity MEMS
(Micro-ElectroMechanical System) sensor technology
and meets the equipment market demand for
integrated vacuum solutions.
Features and benefits
• Wide measuring range, from atmosphere to 10-5 Torr
• Integration with equipment electronics
• Three open collector set points for advanced process control
• User-friendly digital control via host processor or computer
• Analog output with 0.5VDC / decade
• Analog / digital remote zero calibration provides ease of operation
• Ultra compact dimensional design simplifies installation
• Standard DIP 28 pin footprint for easy integration
• RoHS compliant
The 905 MicroPirani™ Sensor Kit is a calibrated plug and play vacuum pressure transducer solution for
OEM system integration. The kit consists of a MEMS-based pressure sensor and a measuring electronics
and processor module. The electronics module fits a standard 28 pin DIP socket and can easily be
integrated on a printed circuit board together with other electronics. The sensor module can either be wired
through the circuit board or connected by a flexible flat cable from the electronics module. The MicroPirani™
sensor element consists of a silicon chip construction, where thermal conductivity is measured in a small
cavity where gas is passed by diffusion instead of flow (see appendix). The MicroPirani™ offers a wide
measuring range of 1-2 decades lower than traditional wire based pirani and convection gauges. The sensor
can be mounted in any orientation without compromise of measurement performance. The advanced
electronics module offers a wide selection of interface possibilities including an analog voltage output of 0.5
VDC / decade, digital communication via TTL UART interface and three independent open collector set
points. The digital interface can transfer real time measuring data directly to a host processor or be used for
configuration of set point parameters and user calibration.
Applications
The 905 MicroPirani™ Sensor Kit can be used in a variety of applications and systems, including:
• Gas analysis – Mass spectrometry
• Scanning electron microscopes
• Vacuum pumping systems
• Gas leak detectors
• Semi surface and thin film analysis
• Space flight systems
• Vacuum valves
• Freeze drying
• UHV gauges
• Gyroscopes

Series 905 Page 4 Design Guide
Applications (continued)
The following are some of the more common applications for the MicroPirani™ Sensor Kit:
Gas leak detection
The portable MKS Pico helium leak detector uses MicroPirani™ sensor kit technology for inlet vacuum
measurement and protection of the helium mass spectrometer.
Figure 1 - MKS Pico helium detector
Mass spectrometers
In a mass spectrometer, the mean distance between molecules must reach a certain distance before
activating the analyzing cell. The MicroPirani™ Sensor Kit can be used to measure pressure and thereby
determine adequate mean free path of molecules. The size of mass spectrometers is constantly shrinking
and the sensor kit significantly reduces space taken by traditional vacuum gauges, allowing more compact
equipment design.
Pumping systems
Traditional vacuum gauges occupy significant space in a pumping system. The compact size of the sensor
kit allow pump manufacturers to integrate vacuum measurement solutions in pumping systems like multi-
stage turbo molecular pumping systems.
Figure 2 - Generic molecular pump
Space flight systems
The low weight and highly robust MEMS sensor design allows use in demanding applications and extreme
environments like equipment for use in space flight. The electronics and sensor element are designed to
withstand the extreme g-forces and intense vibrations experienced during rocket launch.

Series 905 Page 5 Design Guide
905 MicroPirani™ Sensor Kit specifications
Measurement range 1 × 10-5 to 760 Torr1
1 × 10-5 to 1000 mbar
1 × 10-3 to 1 ×10+5 Pascal
Measurement accuracy 5%2
Pressure units (user selectable) Torr, mbar, Pascal
Supply voltage +5VDC (±2%)
Supply current 45 mA
Digital user interface Serial UART, TTL level
Analog output range 0.5 VDC - 4.5 VDC
Analog output impedance 100 Ohms
Set point outputs 3 (open collector)
Set point sink current 50 mA
Operating temperature 5° to 40°C (41° to 104°F)
Storage temperature -10° to 55°C (14° to 131°F)
Sensor bakeout temperature 130°C (266°F)
Material exposed to vacuum Silicon, SiO2, SiN4, Epoxy, Gold
Weight (electronics module) 9 grams
Mounting electronics DIP 28 Pin socket
Mounting electronics pins 0.45 mm diameter
Sensor cable connector Omron Rotary backlock type
P/N: XF2M-1015-1A
0.5mm pitch, 10 pins, gold plated contacts.
Sensor cable Flexible flat cable with 0.5mm pitch and 10 pins.
(See documentation for the cable connector)
Electronics dimensions 47.8 × 20.8 mm (1.882 x 0.820 in)
MicroPirani™ electronics module pinout.
Figure 3 - Electronics module (seen from above)
1. MP Sensor pin1
2. AGND
3. MP Sensor pin2
4. AGND
5. MP Sensor pin3
6. Differential analog Out+
7. Differential analog Out-3
8. Activity LED
9. GND
10. GND
11. μP PSEN
12. Set point 1, open collector
13. Set point 2, open collector
14. Set point 3, open collector
15. GND
16. RS485 enable
17. +5V supply
18. +5V supply
19. Remote zero switch
20. TxD (TTL)
21. RxD (TTL)
22. Microprocessor reset
23. N/C4
24. N/C4
25. N/C4
26. N/C4
27. N/C4
28. N/C4
1Zero offset can impact measurement accuracy in the 10-5 and low 10-4 Torr/mbar decade and consequently
zero adjustment may be required in some applications for repeatable measurement.
2Typical measuring accuracy from 1 × 10-3 to 100 Torr Nitrogen pressure measured at 25°C.
3This pin is actually analog ground, but is referred to as the negative analog output.
4Reserved for future use. Do not connect.

Series 905 Page 6 Design Guide
Electronics module dimensions
Figure 4 - Dimensions: millimeters [inches]
MicroPirani™ sensor and board dimensions
Figure 5 - Dimensions: millimeters [inches]

Series 905 Page 7 Design Guide
About the evaluation board
The MicroPirani™ Sensor Kit is designed for a high level of
integration, but the evaluation board can get the MicroPirani™
sensor kit up and running in minutes. The evaluation board offers
both RS232 and RS485 digital communication and can be
connected directly to a PC for real time pressure data logging and
setup of digital parameters. For easy connectivity, all Sensor Kit
I/O pins are available through screw terminals on the evaluation
board.
The evaluation board is also compatible with the PDR9005
controller which can be used for pressure readout and setup of
digital parameters.
Features and benefits
• Screw terminals for easy hookup to external components (MicroPirani™ sensor / communication etc.)
• RS232 or RS485 communication easily selectable via jumpers.
• Remote zero switch
• Activity LED
• Power supplied via DSUB connector or via screw terminals (jumper selectable)
• Onboard 5V switchmode powersupply with wide voltage range input.
• Microprocessor reset switch (for external watchdog)
• 9 pin DSUB connector for connection to a PDR900 or serial terminal.
Description
The evaluation board is used as a link between the electronics module and a PDR900 or a standard serial
terminal. The board is easily configured using the onboard jumpers and all terminals have associated text
indicating their function.
The evaluation board allows users to quickly evaluate the features of the 905 MicroPirani™Sensor Kit
without having to build an electronic interface from scratch. When the sensor kit is implemented in the
customers system only the electronics module and sensor (with optional cabling) is used.
The serial communication (RS232 or RS485) follows the traditional series 900 transducer command set and
the complete list of commands is located in the command set chapter.
5For more information about the PDR 900, see the following URL:
http://www.mksinst.com/product/product.aspx?ProductID=450

Series 905 Page 8 Design Guide
Evaluation board overview
Connections
The following symbols refer to the picture:
Symbol: Description:
V+ / Gnd Optional power supply connection.
Vsupply Choose supply voltage from the DSUB connector or
screw terminals (Vext).
Activity LED Indicates current system status.
Zero Switch Used to zero the pressure readout at vacuum
Reset Short circuit and release to reset the microcontroller
on the electronics module.
S.Pin1 / 2 / 3 Can be used to connect the MicroPirani™ sensor to the
socket pins of the electronics module. Each sensor
connection has an associated ground connection.
A+ Differential analog+ output.
A - Differential analog- output.
R1 / R2 / R3 Set point outputs.
RxD Data receive pin when configured to external
communication.
TxD Data transmit pin when configured to external
communication.
485 RS485 enable pin.
DSUB 9 pin DSUB communications port.
RxD int / ext Chooses between the ‘RxD’ screw terminal (TTL directly
from the module) or DSUB connector (RS232 or RS485)
as receiver.
TxD int / ext Chooses between the ‘TxD’ screw terminal (TTL directly
from the module) or DSUB connector (RS232 or RS485)
as transmitter.
232 / 485 Chooses between RS232 and RS485 communication.
All three jumpers must be in either the 1-2 or 2-3
position.
Electronics Mount the electronics module here, notch facing board
module edge as shown.
D-SUB male connector pinout
1. <Not used>
2. <Not used>
3. Power supply +
4. Power supply ground
5. Analog output +
6. <Not used>
7. RS232 transmit or RS485-
8. Analog output -
9. RS232 receive or RS485+
Specifications
Supply voltage 9-30VDC via DSUB connector or screw terminals
Dimensions Approx. 48 x 87mm (1.89 x 3.43 in)
Communication RS232 / RS485 (9 pin DSUB) or TTL level (via screw terminals)
Sensor connection Screw terminals or connector on the electronics module
Set point outputs 3 with onboard shunt diodes for use with relays.
Zero switch Onboard
Fi
g
ure 6
–
The evaluation board
Figure 7 - 9 pin D-SUB interface (at the
connector)

Series 905 Page 9 Design Guide
Getting started with the 905 MicroPirani™ Sensor Kit
This guide describes how to install and operate the MicroPirani™ Sensor Kit with the evaluation board. For
a complete description of how to integrate the 905 in a system see the next chapters.
Please read the guide carefully, and note the following:
Make sure power is disconnected before connecting the MicroPirani™ sensor. Otherwise the
MicroPirani™ sensor element will be destroyed. Also, don’t measure the resistors on the sensor
as they will be destroyed by a regular ohmmeter.
Be careful when handling the MicroPirani™ sensor. Never touch the surface of the sensor itself
because the bonding wires are easily damaged.
Installing the electronics module
Unpack the evaluation board and the electronics module. Insert the flexible flat cable into the connector
(marked ‘K2’ on figure 4) on the electronics module, lock it tight, and position the module with the notch
facing the edge of the evaluation board. Gently insert the module into the socket, making sure not to bend
the pins.
Note: The flexible flat cable can be inserted every way possible (both on the electronics module and/or the
sensor board). This has been done to ensure that a correct connection is established regardless of the way
the cable is mounted, which allows total freedom when connecting the sensor to the electronics.
Connecting the electronics module with the sensor
With the power disconnected, insert the flexible flat cable into the connector (marked ‘K1’ on figure 5) on
the sensor board and lock it tight. Mount the KF16 flange on your vacuum system.
Read the chapter “MicroPirani™ electrical connections” for information on how to use the sensor screw
terminals (S.Pin1-3).
Choosing communication standard
Choosing RS232 or RS485 communication is easily done using the jumpers on the evaluation board. There
are three separate jumpers next to the DSUB connector, and these should be in position 1-2 (all three) when
using RS232 and 2-3 (all three) when using RS485:
Note 1: It is not necessary to power off the system in order to change communication standard.
Note 2: Make sure, that the RxD and TxD jumpers are set to ‘Int’. If they are set to ‘Ext’ the communication
doesn’t go through the DSUB connector.
Connecting the communication cable
Connect a suitable cable to the evaluation board and a host system of your choice (don’t turn on the
PDR900 or plug in the power supply at this time). The PDR900 is capable of changing all user commands on
the 905. A standard terminal program can also be used to communicate with the 905 directly.

Series 905 Page 10 Design Guide
Powering up the system
Make sure, that the Vsupply jumper is set to ’DSUB’:
PDR900: Power on the PDR900 and wait a few seconds. The MicroPirani™ Sensor Kit will present itself as
a 905 transducer on the PDR900 display. Refer to the PDR900 manual for configuration and operating
instructions.
Standard terminal: This requires the cable with attached power supply (see ordering information). Plug in
the power supply, and choose the connected communication port (usually COM1 or 2) and set it to 9600bps,
8 bits, no parity, 1 stop bit and no flow control. If possible, turn on “local echo” which enables the user to see
what is being typed.
Type in the following command to verify that the connection is working:
Query: @254MD?;FF
Query Response: @253ACK905;FF
The MicroPirani™ Sensor Kit should return the above statement.
Refer to the chapter “RS232 / RS485 command set” for a complete list of commands.
Analog output
The analog output of the MicroPirani™ Sensor Kit can easily be evaluated with a differential voltmeter
connected to the A+ and A- terminals. See the chapter “Analog Output” for more information on how to utilize
this output.

Series 905 Page 11 Design Guide
Integrating the 905 MicroPirani™ Sensor Kit
This chapter deals with the integration of the 905. Every aspect of the integration is covered, such as how
to connect the sensor and how to choose the external components needed to make the 905 operate at peak
performance.
These major steps need to be completed in order to integrate basic functionality of the 905:
1. Choosing a power supply
2. Making the electric connections of the MicroPirani™ sensor
3. Making the mechanical (vacuum) connection of the MicroPirani™ sensor
4. Establishing communication to/from the electronics module
5. Integrating the electronics module onto a printed circuit board
A thorough description of the above steps follow, as well as the other features of the 905.
Choosing a power supply
The power supply for the 905 should be a stabilized noisefree 5VDC ± 2% supply. There are many types of
switch mode power supplies which will be adequate for this purpose, but avoid charge pump power supplies,
because they generate too much noise on the output. The evaluation board utilizes an LM2594-5.0 IC which
is a Buck (step-down) converter from National Semiconductor. It’s basic configuration can be seen on the
picture below. It can accept a voltage input between 9 and 30V. More information on this, and other, switch
mode IC’s can be found on Nationals homepage.
The 905 can also be driven from a standard linear regulator as long as the voltage stays within the ± 2%
limit and voltage ripple is minimal. Regulator losses are expected to be higher than with switch mode
supplies though, because the efficiency drops from around 80% (or more) to around 50% for linear
regulators, which could be a concern for handheld devices.
Figure 8 - Switch mode power supply based on a National LM2594 IC
The electronics module should be connected to the 5V power supply using pin 17 or 18 (or both) and a
ground connection to pin 15. No further filtering of the 5V supply is needed, as the electronics module has its
own filter to provide the voltage for the analog circuits (for the measurements).
If it is desired to be able to switch the 905 on and off, a power supply with enable pin can be used for this
purpose. The LM2594 has a special ON/OFF pin which makes this easy. If pin 5 is held high the output
voltage will drop to 0VDC until it is pulled low again. This also has the advantage, that it reduces the current
consumption of the LM2594 to <0.5mA.

Series 905 Page 12 Design Guide
MicroPirani™ electrical connections
The MicroPirani™ sensor can be connected to the electronics module in two different ways. The simplest
way is to use the flexible flat cable connector to connect the sensor board to the electronics module, but it’s
also possible to use the pins in the DIP socket instead. If a custom connection is desired, refer to the figure
below when connecting the sensor:
1
2
3
4
5
1
10 1
10
Figure 9 - MicroPirani™ connection details (bottom view of sensor)
The picture also shows the relationship between the DIP socket and the FPC connector. The FPC
connections have been made symmetrical, which eliminates wrong connections with the flexible flat cable.
The analog ground wires are pins 2 and 4 on the DIP socket, and 1,2,9 and 10 in the FPC connector.
The evaluation board has screw terminals to quickly connect a sensor to the electronics module. The
designation (on the evaluation board) ‘S.Pin1’ (sensor pin 1) corresponds to pin 1 on the electronics module,
S.Pin2 to pin 3 and S.Pin3 to pin 5, respectively. The ‘MPGND’ connections connect to pins 2 and 4 on the
electronics module.
This is how the pins on the MicroPirani™ have been placed:
Figure 10 - MicroPirani™ sensor connections (bottom view)
The cable or printed circuit board connections between the MicroPirani™ sensor and the electronics
module can be chosen arbitrarily in length, but keep the distance as short as possible to avoid noise to
interfere with the pressure measurements. It is not possible to specify a maximum cable length as this
depends on the system in question. The MicroPirani™ sensor is especially sensitive when measuring at
vacuum (and atmospheric pressure). The entire 10-5 decade (Torr / mbar) only spans around 1mV. The
following are general guidelines when using the different connections:
Flexible flat cable
The flexible flat cable fits directly in the connector on the electronics module and provides a firm connection
of the MicroPirani™ sensor. Use the cable provided by MKS or a 10 pin FFC cable with 0.5mm pitch and
gold plated contacts. See the specifications for the P/N of the connector the cable should be made to fit in.
Shielded flexible flat cables exist, and could be necessary if the 905 is to be used in very noisy
environments. Under normal circumstances a regular flexible flat cable will suffice.

Series 905 Page 13 Design Guide
Regular cable
A regular round cable can be used if the DIP socket connections have been chosen, but the printed circuit
board (where the electronics module is mounted) does not extend all the way to the sensor. Use a shielded
cable if possible and optimise for minimal length to minimise measuring noise.
Printed circuit board connection
If a connection through a printed circuit board is desired to connect the MicroPirani™ sensor to the
electronics module, there are a few rules to follow. The sensor wire traces should be kept closely together on
the same side of the printed circuit board, and an analog ground plane should cover the underside of the
traces. If the signals are allowed to flow close to digital signals, or digital power planes, measuring noise
could result from this.
Refer to figure 9 when laying out connections between the MicroPirani™ sensor and the electronics
module. The connections should be kept close together and a trace width of minimum 0.3mm (0.012 inches)
is recommended. Below these wires an analog ground plane (/copper area) should be layed out and it
should cover the sensor connection traces. The analog ground plane should be connected to pin 2 and 4 on
the electronics module and not the sensor grounds, to avoid ground loops. Also, do not connect this
groundplane to the ground found on pins 9 and/or 10.
)
The MicroPirani™ and the electronics module have been calibrated as a matched pair. It is not
possible to interchange sensor or electronics module without a complete factory recalibration.
Installing the MicroPirani™ sensor
The MicroPirani™ sensor can be mounted in any direction because the sensor was designed to minimize
convection so that the operation is possible in any position without compromising accuracy. It should be
located where it can measure chamber or manifold pressure. Install it away from pumps and gas sources
and where vibration is minimal. Also, locate and orient the 905 where contamination is least likely. Avoid
installation where the sensor could be contaminated, such as above a roughing pump where oil vapor could
enter the MicroPirani™ and cause the calibration to shift.
The recommended sensor hole dimensions are on the following picture. Note the small hole leading to the
cavity where the MicroPirani™ is located. This has been done to mechanically shield the sensor from
possible heat sources which could lead to wrong pressure readings. Always avoid direct line-of-sight heat
sources.
Figure 11 - Mounting hole (seen from above)
Figure 12 - Mounting hole (side view)
When mounted this way the sensor o-ring has been compressed to achieve a tight fit with about 30%
compression. We generally recommend between 20 and 30% compression.The sensor board is then flush
with the surface which ensures that the o-ring can not be overstrained when tightening the mounting screws.
)
Note: Mount the o-ring on the MicroPirani™ sensor before
assembly, not in the groove of the mounting hole.
After the assembly of the complete vacuum setup it’s important to leak
test the system. Helium is suitable for probing a system which pumps air
or nitrogen. If the MicroPirani™ installation is found not
to be vacuum tight there are a few causes worth mentioning:
•Dirt on the o-ring (for instance a hair). Clean or replace o-ring and groove.
•O-ring damaged due to incorrect mounting. Replace o-ring.
•Screws not fully tightened. The sensor board spacer should be flush with the surface.
Figure 13 - Mounted sensor

Series 905 Page 14 Design Guide
Communication
The electronics module sends and receives TTL level signals direcly from the microcontroller. How these
signals should be integrated with the rest of the setup depends on the user configuration and application.
If the 905 is to communicate directly with another microcontroller no signal conversion is necessary and
TxD/RxD (pins 20 and 21 respectively) can be connected directly. This means, that the communication is
TTL level all the way.
If the 905 is to be hooked up using an RS232 connection then a driver IC (transceiver) is to be used. This
can be achieved with a standard RS232 transceiver IC. These ICs have built-in voltage conversion, which
only requires external capacitors (usually between 1 and 4 pcs.).
The 905 can also be used on a RS485 network with half duplex capability. This requires the use of
RS485_ENABLE (pin 16) and the purpose of this pin is described in the following section.
Example configuration for RS232 and RS485
The evaluation board utilizes an IC which is capable of both RS232 (full duplex) and RS485 (in half duplex
mode) communication. The LTC1387 from Linear Technology is ideal for this purpose, because it can be
configured for both types of communication with three pins.
Figure 14 - RS232 configuration
Figure 15 - RS485 configuration
The picture above shows the configuration for each type of communication. To configure for RS-232 mode
connect the IC as shown on the first picture. This provides one master and one slave.
To configure for RS485 communication use the setup on the second picture. The change between these
two states have been implemented using jumpers on the evaluation board, but the pins can also be
connected to the host system, making it capable of changing the state.
The signal ‘RS485_ENABLE’
When using RS485 communication the RS485_ENABLE signal must be used. This signal is a logical '1'
when the electronics module is driving the RS485 network and a logical ‘0’ at all other times. When
RS485_ENABLE is active (high) only this device is able to send on the network. When RS485_ENABLE is
inactive (low) the output of the transceiver is tristated6and other devices are able to send data. The 905 is
configured to always listen for commands on the network and respond if the correct address is spoken to.
6An output on an integrated circuit can be in one of three states: low, high or tri-stated. When tristated the
output does not pull the signal in either direction so it does not interfere with signals using the same wire.

Series 905 Page 15 Design Guide
Analog Output
The analog voltage output can be used for connection to external analog measuring equipment for pressure
reading and data logging. The analog output must be connected to a true differential input voltmeter or an
analog to digital (A/D) converter with a differential input in a system controller.
The analog output will change scale when the pressure unit is changed and will always provide 0.5VDC per
decade whether Torr, mbar or Pascal is selected.
Figure 16 - Correct setup Figure 17 - Incorrect setup
Note: Do not connect the negative side of the analog output to the chassis / ground or to any other ground.
Measurement errors in the output voltage may be seen due to the voltage drop from this current loop flow.
The longer the cable, the worse the error will be.
If the analog output is improper connected, shorted to ground or heavily loaded, the pressure transducer
performance and consequently pressure reading can be affected.
The graph below shows the correlation of linear analog output to pressure.
To calculate pressure (Torr/mbar) from voltage: )-Vout(
out
VP 62 10)( =
To calculate pressure (Pascal) from voltage: )-Vout(
out
VP 42 10)( =
To calculate voltage from pressure (Torr/mbar): 2
6
(+ =Log(P) P)
out
V
To calculate voltage from pressure (Pascal): 2
4
(+ =Log(P) P)
out
V
Figure 18 - Analog output (in VDC) vs. pressure (in Torr / mbar)

Series 905 Page 16 Design Guide
Pressure to voltage table
Utilization of remote zero
The electronics module has a remote zero function (pin 19) which allows the user or system setup to
manually perform zero adjustment. Pressing remote zero on the evaluation board is equal to sending the
VAC-command as described in the command set. The zero adjustment should be performed when at a
pressure lower than 8 × 10-6 Torr.
When a zero adjustment is required, simply pull the zero switch pin low briefly, or send the VAC-command.
The activity LED will blink twice if the calibration was successful, and once if the pressure was too high for
calibrating zero. On the evaluation board the switch simply connects the pin to ground when pressed down.
Pressure
[Torr/mbar]: Output [V] Pressure [Torr/mbar] Output [V]
1.0 × 10-5 0.500V 1.0 × 10-1 2.500V
2.0 × 10-5 0.651V 2.0 × 10-1 2.651V
4.0 × 10-5 0.801V 4.0 × 10-1 2.801V
6.0 × 10-5 0.889V 6.0 × 10-1 2.889V
8.0 × 10-5 0.952V 8.0 × 10-1 2.952V
1.0 × 10-4 1.000V 1.0 × 1003.000V
2.0 × 10-4 1.151V 2.0 × 1003.151V
4.0 × 10-4 1.301V 4.0 × 1003.301V
6.0 × 10-4 1.389V 6.0 × 1003.389V
8.0 × 10-4 1.452V 8.0 × 1003.452V
1.0 × 10-3 1.500V 1.0 × 10+1 3.500V
2.0 × 10-3 1.651V 2.0 × 10+1 3.651V
4.0 × 10-3 1.801V 4.0 × 10+1 3.801V
6.0 × 10-3 1.889V 6.0 × 10+1 3.889V
8.0 × 10-3 1.952V 8.0 × 10+1 3.952V
1.0 × 10-2 2.000V 1.0 × 10+2 4.000V
2.0 × 10-2 2.151V 2.0 × 10+2 4.151V
4.0 × 10-2 2.301V 4.0 × 10+2 4.301V
6.0 × 10-2 2.389V 6.0 × 10+2 4.389V
8.0 × 10-2 2.452V 8.0 × 10+2 4.452V
1.0 × 10+3 4.500V