MKS MicroPirani 925 Series Specification sheet

925 MicroPirani™ Operation Manual
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925 MicroPirani™
Vacuum Pressure Transducer
Models with RS-232/RS-485,
EtherCAT®, or Digital Display
Operation and Installation Manual
P/N: 100017129
925 MicroPirani™ Transducer
Operation and Installation Manual
Revision: K, February 2020

925 MicroPirani™ Operation Manual
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Service and Warranty Guidelines
Notice
This product is intended for use by industrial customers and should be
serviced only by MKS trained representatives. The service manuals and
related materials are provided in English at no charge and are intended for
use by experienced technicians. It is the responsibility of the user to obtain
and assure the accuracy of any needed translations of manuals. If you
require assistance, contact the MKS Customer Service group. The MKS
Technical Support Group notifies users of record if safety-related upgrades
or new hazards associated with the product are identified.
Damage Requiring Service
Disconnect the product from all power sources and refer servicing to Qualified Service Personnel under the
following conditions:
a. When any cable or plug is damaged.
b. If any liquid has been spilled onto, or objects have fallen into the product.
c. If the product has been exposed to rain or water.
d. If the product does not operate normally even if you follow the operating instructions. Adjust only those
controls that are covered by the operation instructions. Improper adjustment of other controls may result in
damage and will often require extensive work by a qualified technician to restore the product to its normal
operation.
e. If the product has been dropped or the enclosure has been damaged.
f. When the product exhibits a distinct change in performance. This indicates a need for service.
Service and Warranty
Some minor problems are readily corrected on site. If the product requires service, contact the MKS Technical
Support Department at [phone]. If the product must be returned to the factory for service, request a
Return Material Authorization (RMA) from MKS. Do not return products without first obtaining an RMA. In some
cases, a hazardous materials disclosure form may be required. The MKS Customer Service Representative will
advise you if the hazardous materials document is required.
When returning products to MKS, be sure to package the products to prevent shipping damage. Shipping damage
on returned products due to inadequate packaging is the Buyer's responsibility.
Customer Service / Technical Support:
MKS Global Headquarters
2 Tech Drive, Suite 201
Andover MA, 01810 USA
Phone: [phone]
Email: [e-mail]
Visit our website at: www.mksinst.com
Warranty Information
MKS Instruments, Inc. provides an eighteen (18) month warranty from the date of shipment for new MKS products.
The MKS Instruments, Inc. general terms and conditions of sale provide the complete and exclusive warranty for
MKS products. This document is located on our web site at www.mksinst.com, or may be obtained by a contacting
an MKS customer service representative.

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Proprietary Information
This document contains confidential proprietary information belonging to MKS Instruments, Inc. This information is
not for publication and has been provided to MKS on the condition that it not be copied, reproduced or disclosed,
either wholly or in part, to third parties without the expressed written consent of MKS Instruments, Inc.
The information contained in this document is subject to change without notice.
Copyright Information
© 2020 MKS Instruments, Inc. All rights reserved. Granville-Phillips® is a registered trademark of MKS
Instruments, Inc., and mksinst™, DualTrans™, MicroPirani™, UniMag™, DualMag™, TriMag™, and
QuadMag™ are trademarks of MKS Instruments Inc. Windows® is a trademark of Microsoft Corporation.
All other trademarks and registered trademarks are the properties of their respective owners.
No part of this work may be reproduced by any method including photocopying and recording or by any
information or retrieval system without written permission of MKS Instruments, Inc.
Table of Contents
Warranty Information ......................................................................................................................................... 2
Proprietary Information ...................................................................................................................................... 3
Copyright Information ......................................................................................................................................... 3
Symbols used: ................................................................................................................................................... 4
Unpacking .......................................................................................................................................................... 5
Description ......................................................................................................................................................... 6
925 Functions .................................................................................................................................................... 7
User Switch (RS-232/RS-485 models only) ....................................................................................................... 7
LED Status Indicator .......................................................................................................................................... 7
EtherCAT Status Indicator ................................................................................................................................. 7
Transducer installation (mechanical) ................................................................................................................. 8
Transducer installation (electrical) ..................................................................................................................... 9
Serial user interface ......................................................................................................................................... 12
Communication Protocol .................................................................................................................................. 13
Setpoint relays ................................................................................................................................................. 15
Integrated Touch Display (not available in EtherCAT units) ............................................................................ 17
Calibration and adjustment .............................................................................................................................. 20
Factory defaults ............................................................................................................................................... 22
Transducer lock function (not available on EtherCAT units) ........................................................................... 23
User Switch Command (not available on EtherCAT units) .............................................................................. 23
Transducer test (not available on EtherCAT units) .......................................................................................... 23
Status Query Commands ................................................................................................................................. 24
Analog output ................................................................................................................................................... 25
MicroPirani gas dependence ........................................................................................................................... 46
Query Command list ........................................................................................................................................ 49
Setup and configuration command list ............................................................................................................. 50
Firmware upgrades (RS-232 only) ................................................................................................................... 51
FAQ (Frequently Asked Questions .................................................................................................................. 52
Troubleshooting ............................................................................................................................................... 54
Service and Repair .......................................................................................................................................... 55
Specifications ................................................................................................................................................... 57
925 Transducer Dimensions ............................................................................................................................ 59
Accessories and replacement part numbers ................................................................................................... 61
Index ................................................................................................................................................................ 63

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Safety information:
Symbols used:
The first symbol below is used throughout this manual to further define the safety concerns associated with the
product. The last two symbols identify other information in this manual that is essential or useful in achieving
optimal performance from the 925 MicroPirani™ transducer.
Caution:
Failure to read and follow the message could result in personal injury
or serious damage to the equipment or both.
Critical:
Failure to read and follow the message could result in damage to the
equipment.
Attention:

Calls attention to important procedures, practices, or conditions.
General safety information
The safety instructions should always be followed during installation and operation of the 925 MicroPirani™
transducer. Pass safety information to all users.
Safety Precautions:
Electrical connections. The 925 must be properly electrically connected to perform
according to the specifications.
Output pins are not protected against wrong electrical connections. Wrong electrical
connections can cause permanent damage to the transducer or interference to measuring
performance.
Refer to Electrical connections description, beginning on page 9.
Fuse. The 925 power supply input has an internal thermal fuse. The fuse is self
recoverable and should not be changed.
Explosive Environments. Do not use the 925 in presence of flammable gases or other
explosive environments.
Corrosive Environments. The 925 is not intended for use in corrosive environments.
Refer to Transducer installation, beginning on page 8.
Service and Repair. Do not substitute parts or modify instrument other than described in
Service and Repair on page 55. Do not install substituted parts or perform any
unauthorized modification to the instrument. Return the instrument to an MKS Calibration
and Service Center for service and repair to ensure all of the safety features are
maintained.

CE marking The 925 transducer complies with European standards for CE
marking.

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Unpacking
Before unpacking the 925 MicroPirani transducer, check all surfaces of the packing material for shipping damage.
Inspect for visible damage. If found, notify the carrier immediately.
Check to be sure the 925 package contains these items:
Part number
Description
925-xxxxx
925 Transducer
100017128
Quick Start Guide
If any items are missing, call MKS Customer Service at [phone] or your local MKS
sales office or distributor.
Part Number
The 925 MicroPirani part number system has 5 digits that identify flange, communication interface, analog output
type, I/O connector and sensor sealing type. Transducers can be delivered preconfigured with various parameters
pre-programmed like setpoint settings. These specials have an additional 4 digits after the regular part number.
Transducer Model ....................................................... Code
925 MicroPirani™ ......................................................... 925-
Flange
KF16 ......................................................................... 1
KF25 ......................................................................... 2
1/8'' NPT-M .............................................................. 3
VCR4 ........................................................................ 4
VCR8 ........................................................................ 5
CF1.33 ..................................................................... 6
KF16 extended ......................................................... 8
Interface
RS232/Analog .......................................................... 1
RS485/Analog .......................................................... 2
EtherCAT/Analog ..................................................... 7
Analog Out
Standard MKS .......................................................... 0
Connector Relays
Sub D 9 pin male/1 relay set point ........................... 1 (not available with EtherCAT)
Sub D 15 pin HD male/no relay ............................... 2
Sub D 15 pin HD male/3 relays ................................ 3 (not available with EtherCAT)
Sub D 15 pin HD male/3 relays/Dual A out .............. 5 (not available with EtherCAT)
Enclosure Sealing
Standard/Viton sealing ............................................. 0
Standard/Viton sealing/display ................................. 4 (not available with EtherCAT)
(Ordering Code Example: 925-11030 = KF16, RS232, standard analog output, Sub D 15 pin HD male,
3 relays, Viton.)
Analog Output
The 925 has a standard analog output voltage pressure signal of 1VDC/decade, but it can also emulate analog voltage outputs
from a variety of other vacuum transducers. The emulation feature can be used to upgrade and replace other vendors gauges in
OEM applications without changing system software. Contact MKS customer service for details.
The standard 925 uses a 15 pin HD sub D connector, but it is also available with connectors offered by other vendors.
Special versions
Part number
925-x7020 EtherCAT option, flange only

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Description
The 925 MicroPirani™ vacuum transducer offers a wide measuring range from 1×10-5 Torr to atmosphere and is
based on measurement of thermal conductivity.
It can be used in a variety of applications as standalone unit or with the
PDR900 display and controller unit. (not available in EtherCAT units)
The transducer has RS-232 or RS-485 digital communication interface for
setup of transducer parameters and to provide real time pressure
measurement.
NOTE: The EtherCAT®model is not compatible with the PDR900.
The 925 has up to three mechanical relays (not available in EtherCAT units) which can be used for process control
like for example interlocking valves or pumps. The analog voltage output can be interfaced to external analog
equipment for pressure readout or controlling.
Sensor technology
The 925 transducer has a single MicroPirani sensor element and it’s based on
measurement of thermal conductivity. The MicroPirani sensor consists of a silicon chip
with a heated resistive element forming one surface of a cavity. A cover on top of the
chip is forms the other surface of the cavity. Due to the geometry of the sensor
convection cannot take place within the cavity and consequently the sensor is
insensitive to mounting position. Gas molecules are passed by diffusion only to the
heated element where the heat loss of the gas is measured.
The sensor element is very robust and can withstand high G-forces and instant air
inrush.
Applications
The 925 can be used in many different vacuum applications within the semiconductor, analytical, and coating
industries:
• General vacuum pressure measurement
• Fore line and roughing pressure measurement
• Gas backfilling measurement and controlling
• Mass spectrometer control
• Activation of UHV gauge
• System process control
• Sense abnormal pressure and take appropriate security measure using relay set points
(not available in EtherCAT units)
• Control system pressure
Disposal (European Union only)
The 925 transducer is manufactured according to the RoHS directive.

For the benefit of the environment, at the end of life of the 925, it should not be
disposed in the normal unsorted waste stream. It should be deposited at an
appropriate collection point or facility to enable recovery or recycling.
Temperature measurement
resistors Rt
Silicon cover
Silicon cover
Measuring
resistors Rm

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925 Functions
User Switch (RS-232/RS-485 models only)
The user switch has the following functions:
1. Vacuum Zero adjustment (VAC! Command)
2. Atmospheric adjustment (ATM! Command)
3. Transducer firmware upgrade mode

If the user switch is activated by accident and vacuum Zero or Atmospheric adjustment is executed
the original factory adjustment can be recovered using the FD!VAC or FD!ATM command. (See
Factory defaults on page 22).

If the transducer is delivered with customer specified parameters the User Switch is disabled. For
enabling the switch, see page 23.
LED Status Indicator
The red/green LED status indicator has the following stages:
LED Color
Flash Interval
Status
GREEN
Solid
Normal operation
RED
2 sec
Power on sequence
GREEN
1 sec
Test mode TST!ON (see page 22)
GREEN flash
3 flashes
User Adjustment executed successfully
RED flash
3 flashes
User Adjustment failed
RED
2 sec
User switch disabled
RED
Solid
Transducer defect
OFF
Firmware upgrade mode (see page 51) or Power OFF
EtherCAT Status Indicator
GREEN
LED
Flash Interval
EtherCAT State
RED LED
Flash Interval
EtherCAT State
OFF
Initialization
OFF
No Error
Blinking
200 ms
Pre Operational
Blinking
200 ms
Invalid Configuration
Single
Flash
100 ms ON
1000 ms OFF
Safe Operational
Flickering
50 ms ON
50 ms OFF
Invalid Firmware
Flickering
50 ms ON
50 ms OFF
Bootstrap
Single Flash
100 ms ON
1000 ms OFF
Unsolicited State Change
ON
Operational
Double Flash
Application Watchdog
Timeout
ON
PDI Watchdog Timeout

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Transducer installation (mechanical)
Do not use or install the 925 transducer where the following conditions occur:
- Temperatures lower than 0 oC or higher than 40 oC
- Corrosive or explosive gases
- Direct sunlight or other heat sources
Process compatibility
The 925 transducer is intended for use in relatively clean environments. The transducer cannot be used in
corrosive environments like a semiconductor etch process camber where aggressive gases like fluorine are used.
If the 925 transducer is located close to a gas source connection like a flow controller or leak valve the transducer
pressure measurement can be higher than the actual chamber pressure. Location close to a pumping system
connection can cause a lower pressure measurement than actual chamber pressure.
The 901P transducer can be mounted in any orientation without compromising
performance or accuracy. However it is recommended that the transducer
not be mounted with the flange port facing upwards to avoid contamination
particulates or liquids from entering the device.
Explosive Environments
The MicroPirani sensor filament is kept at a low temperature of only 35 oC above
ambient temperature. However, in case of a malfunction the sensor element can
exceed normal operating temperature and consequently the transducer should
not be used in explosive environments.
Temperature
The 925 has an active and individual sensor temperature compensation circuit
that ensures accurate measurement in a wide temperature range.
For best measuring performance avoid large temperature gradients and direct cooling like air-condition air stream
or heating like a pump exhaust stream.
Bake out
The transducer electronics can withstand 80 oC (176 oF) when the power is turned off.
Contamination
Locate and orient the 925 where contamination is least likely. The MicroPirani sensor has a low filament
temperature of only 35 oC above ambient temperature; therefore, the MicroPirani is less prone to contamination by
cracking products from fore vacuum pump oil.

If the transducer is backfilled with a liquid like pump oil the sensor element is likely permanently
damaged. The transducer cannot be cleaned using solvents.
Vibrations and instant air inrush
The 925 sensor element is extremely robust to mechanical forces like vibration and G-forces. The sensor element
cannot be damaged by fast and repeated pressure cycles or instant inrush of air.
Vacuum connections
The 925 transducer is available with different types of vacuum fittings. When mounting the transducer always
ensure that all vacuum sealing items and surfaces are clean, without damage and free of particles. Do not touch
the vacuum flange sealing surface.
If the transducer will be exposed to pressures above atmospheric pressure make sure that proper
vacuum fittings are used. Ensure that the internal system pressure is at ambient pressure conditions
before opening the vacuum system and removing any connections.
Pressure range
The standard 925 transducer is internally sealed with elastomer Viton sealing and is intended for use in the
pressure range 1×10-5 to 1000 Torr. If used in UHV applications the out gassing rate from Viton® can be too high.

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Transducer installation (electrical)
The 925 is available with different input/output connectors. Use a cable with strain relief to ensure proper electrical
connection and to reduce stress on the connectors.

Ensure a low impedance electrical connection between the 925 transducer body and the
grounded vacuum system to shield the sensor from external electromagnetic sources.
Ensure that the analog output is connected to floating input.
Connect a braided cable to the metal hoods at both ends of the cable with the end for power supply connected to
Earth ground.
The power supply input is 9 to 30 VDC. The power supply input is protected by an internal thermal fuse. The fuse is
self-recoverable; do not replace it. Damage may occur to the circuitry if excessive voltage is applied, polarity
reversed, or if a wrong connection is made.
If using the analog voltage output, connect the positive analog out and negative analog out pins to a differential
input voltmeter or an analog-to-digital (A/D) converter. Do not connect the negative side of the analog output to the
negative side of the power supply input or to any other ground. Doing so will cause half of the power current to flow
through this wire. Measurement errors in the output voltage may be seen due to the voltage drop from this current.
The longer the cable, the worse the error will be. Do not connect the set point relay terminals to the analog output.
Correct connection of analog output to floating input
Incorrect connection of analog output to none floating input

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Input/Output Wiring
Connect braided cable to the metal hoods at both ends of the cable with the end for the power supply
connected to Earth ground.
925 I/O Connector (9 pin)
9 pin male DSUB
PIN
Description
1
Relay, Normally Open
2
Relay, Normally Closed
3
Power + (9-30VDC)
4
Power return -
5
Analog Output +
6
Relay, Common
7
RS-485- / RS-232 Transmit
8
Analog Output -
9
RS-485+ / RS-232 Receive
925 I/O Connector (15 pin)
15 pin male HD DSUB
PIN
Description
1
RS-485- / RS-232 Transmit
2
RS-485+ / RS-232 Receive
3
Power + (9-30VDC)
4
Power return -
5
Analog Output +
6
Analog Output -
7
Relay 1, Normally Open
8
Relay 1, Common
9
Relay 1, Normally Closed
10
Relay 2, Normally Closed
11
Relay 2, Common
12
Relay 2, Normally Open
13
Relay 3, Normally Closed or
Analog Out 2 (Hardware option)
14
Relay 3, Common
15
Relay 3, Normally Open
925P EtherCAT 15 pin
I/O Connector
15 pin male HD D-Sub
PIN
Description
1
NC (No Connection)
2
NC
3
Power + (9-30 VDC)
4
Power return -
5
Analog Output +
6
Analog Output –
7
NC
8
NC
9
NC
10
NC
11
NC
12
NC
13
NC
14
NC
15
Chassis Ground

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EtherCAT I/O Connectors
925 I/O Connector
(6 pin Hirschmann)
PIN
Description
1
Identification resistor (3K)
2
Analog Output +
3
Analog Output –
4
Power + (9-30VDC)
5
Power return -
6
Chassis
925 I/O Connector
(8 pin RJ45/FCC68)
PIN
Description
1
Power + (9-30VDC)
2
Power return -
3
Analog Output +
4
Identification resistor(1)
5
Analog Output -
6
Set point output
7
Not Connected
8
Not Connected
925 RS-232 connector
(6 pin Hirschmann +
8 pin RJ45/FCC68)
PIN
Description
1
RS-232 Transmit
2
RS-232 Ground
3
RS-232 Receive
4
RS-232 Receive
5
RS-232 Ground
6
RS-232 Transmit
P/N: 10001367 RS-232 Cable for Hirschmann and RS45/FCC68 Transducers.
(1) ID resistor depends on part number:
925-xx4x 27K
925-xx4x-0073 71.5K
925-xx8x 36K

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Serial user interface
The standard 925 is supplied with RS-232 or RS-485 user interface. The user interface allows change of transducer
parameters such as set point settings and calibration.
The serial interface uses the following format: 8 data bits, 1 stop bit and no parity bit.
RS-232 user interface
The 925 is DCE (Data Communication Equipment) and can
be connected to DTE (Data Terminal Equipment), typically a
PC.
The serial communication does not use hardware handshake.
The RS-232 standard does not specify the maximum cable
length, but length depends on environment, cable quality and
communication speed. In general cable span shorter than
15m (50ft.) does not require any extra precautions.
The RS-232 connection on transducers delivered with 6 pin Hirschmann and 8 pin RJ45 connector is available at a
separate connector. Refer to Accessories and Replacement part number page for RS-232 programming cable. The
connector is located under the label on the top of the transducer.
RS-485 user interface
RS-485 is a network communication system that enables the
user to communicate with several units on the same
communication line.
RS-485 is a balanced communication system, because signal
on one wire is ideally the exact opposite of the signal on the
second wire. Compared to RS-232 communication RS-485
allows significantly longer cable span. The maximum length
of cable span depends on environment, cable quality and
communication speed, but relative long cable spans up to
1,200m (4,000 ft.) is possible.
There are 2 wires, other than ground, that are used to
transmit the digital RS-485 signal. The 925 uses half duplex
communication.

Always use high quality shielded data cables for serial communication. For long cable runs
use twisted pairs. See also Accessory and replacement part number page 60.
The EIA-485 and NMEA standards specification states that signal A is the inverting “-“and signal B is the non-
inverting or “+”. This is in conflict with the A/B naming used by a number of differential transceiver manufacturers,
that are incorrect, but their practice is used throughout the industry. Therefore, care must be taken when using A/B
naming. In addition to the A and B connections, the EIA standard also specifies a third interconnection point called
C, which is the common ground.
At high communication baud rates and when using long cable runs a termination resistor of typical 120 Ohm should
be connected between pin 1 and 2 at the 925 DSUB connector and between pin A and B at the data
communication equipment. The termination resistors provides low impedance that reduces the sensitivity to
electrical noise and prevents data reflection that can cause data communication corruption.
RS-485 twisted pair cable run with 120Ω terminator resistors (925 with 15 pin connector)
When connecting multiple devices in a RS-485 network make sure that proper guidelines and
specifications are followed to ensure optimal communication performance of the 925.
Improper network design can cause data communication interruption and data collision.

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Communication Protocol
The 925 transducer command set allows the user to change transducer parameters and receive pressure
measurements. Settings and parameters like set point values, set point configurations and calibration data are
stored in the transducer’s non volatile memory.
EtherCAT Communication Protocol: Refer to the EtherCAT Instruction Manual #20003335, which can be
downloaded from the MKS website. Go to www.mksinst.com and search for 20003335.
Communication software
Communication software is required to communicate from a PC via RS-232/485
interface to the transducer. In the standard Microsoft Windows package the hyper
terminal software can be used to type and transmit serial commands to the
transducer. To the right is illustrated the Windows communication port properties for
communicating with transducer factory default settings.
MKS also offers communication software examples that can be downloaded at:
www.mksinst.com/vtsw/
In OEM applications transducer communication software routines are normally
integrated with other system control software.
Query and Command Syntax
Queries return current parameter settings; commands change the parameter setting according to the value the user
enters into the command syntax. Each query or command must begin with the attention character @ and end with
the termination ;FF.
Command syntax for an information query:
@<device address><query>?;FF
Command syntax for a command:
@<device address><command><parameter>?;FF
The command set allows upper and lower case ASCII characters.
Response Syntax (ACK/NAK)
The ASCII characters 'ACK' or 'NAK' preface the query or command response string. The ACK sequence signifies
the message was processed successfully. The NAK sequence indicates there was an error.
The response to a query or a successful command is:
@<device address>ACK<data>;FF
The response to a message with an error is:
@<device address>NAK<NAK code>;FF
Examples:
ACK response: @253ACK9600;FF (baud rate changed to 9600)
NAK response: @253NAK160;FF (command had an error—possible typo)
The following list provides descriptions of the NAK codes that may be returned.
NAK Code Error description Example
8 Zero adjustment at too high pressure @253VAC!;FF
9 Atmospheric adjustment at too low pressure @253ATM!7.60;FF
160 Unrecognized message @253S%;FF
169 Invalid argument @253EN1!of;FF
172 Value out of range @253SP1!5.00E+9;FF
175 Command/query character invalid @253FV!;FF
180 Not in setup mode (locked) -

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Baud rate (not available in EtherCAT units)
The baud rate represents the communication speed. The 925 supports 4800, 9600, 19200, 38400, 57600, 115200
and 230400 baud rates. The transducer is always delivered with factory default baud rate value: 9600.
Change of Baud rate:
Command: @253BR!19200;FF
Command values: 4800, 9600, 19200, 38400, 57600, 115200, 230400
Command reply: @253ACK19200;FF
Factory default: 9600
The transducer will reply in the current baud rate and then change to the new value.
Addressing (not available in EtherCAT units)
The transducer uses an addressable communication protocol that allows multiple MKS 900 Series transducer
devices to be connected in a RS-485 network. The address is required in both RS-232 and RS-485 communication.
The address can be set from 001 to 253. Address 254 and 255 are universal addresses, which can be used to
broadcast a command to all devices on the network. Commands sent with address 254 will be executed by all
transducers on the network and all transducers will transmit a reply. Commands sent with address 255 will be
executed by all transducers on the network, but the transducers will not transmit replies. For example, use address
254 to communicate with a device if its address is unknown.
Change of Address:
Command: @253AD!123;FF
Command values: 001 to 253
Command reply: @253ACK123;FF
Query: @253AD?;FF
Query reply: @253ACK253;FF
Factory default: 253
Communication delay (RS-485) (not available in EtherCAT units)
The 925 half duplex RS-485 interface requires that data is transmitted and received on the same communication
line. Some RS-485 transceiver equipment has a settling time when changes from transmit to receive mode. If the
transducer replies too fast the first character(s) will not be received as the following example illustrates:
Sending pressure request: @254PR1?;FF
Receiving data: .23E-4;FF (Correct data: @253ACK1.23E-4;FF)
The RS delay introduces a baud rate dependent delay between receive and transmit sequence to prevent loss of
data in the receiving string.
Communication delay:
Command: @253RSD!ON;FF
Command values: ON, OFF
Command reply: @253ACKON;FF
Query: @253RSD?;FF
Query reply: @253ACKON;FF
Factory default: ON

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Setpoint relays (not available in EtherCAT units)
The 925 has up to 3 mechanical relays that can be used to control external process equipment. The relay has
closing and breaking contacts and the contacts are rated 30 VDC, 1A, resistive load.
If the transducer is supplied without setpoint relays, the setpoint commands can still be accessed. Refer to part
number definition on page 5 to verify if setpoint relays are included.
Inductive relay load
Special precautions should be taken when driving inductive loads with the relay contact. When an inductive load
like a solenoid is energized, the in-rush current is significantly higher than the regular load current. In-rush currents
exceeding the relay contact rating can cause reduction of relay contact life time or contact reliability.
When a solenoid is de-energized, the collapsing magnetic field can cause significant voltage spikes. These spikes
can couple capacitively from cable to cable and interfere with measuring electronics or transducer signal.
Driving inductive loads via the setpoint relay contacts requires de-energizing spike
protection. Inadequate protection can cause permanent damage to the transducer
or interfere with the analog output signal.
Always ensure that inductive in-rush currents do not exceed relay contact rating.
An arc suppression network, as shown schematically to the right, is
recommended. The values of the capacitance C and the resistance R
can be calculated by the following equations:
C = I2/(1 x 107) R = E/ Ia
where:
C is in Farads. R is in ohms
I is DC or acpeak load current in amperes. E is DC or acpeak source voltage in volts
a = 1 + (50/ E)
Note that Rmin = 0.5 Ωand Cmin = 1×10E-9 F, D is a fast transient suppression diode.
PDR900 controller relays (not available in EtherCAT units)
The PDR900 controller has power relays that can drive higher current loads and voltage than the transducer relays.
If the transducer is used with the PDR900 controller refer to PDR900 manual for setup of relay output.
Do not connect any external sources to the transducer relay pins when using it
together with the PDR900 controller. Always use the PDR900 relay outputs.
Setpoint functionality
The set point relays can be activated either above or below the set point values. The graphs below show the
different relays stages in either below or above configuration. The NC contact will always be closed in case of
power failure.

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Setpoint 1 value
5.00E-3 Torr
Hysteresis 1
6.00E-3 Torr
Setp.1 Direction
Below
Setp.1 Enable
ON
When using the setpoint relay to control process equipment always take
appropriate precautions to prevent system damage in case of transducer power
failure. The NC contact will be closed in case of transducer power failure.

If the transducer is supplied as a special version (p/n: 925-xxxxx-xxxx) with pre-configured
parameters such as setpoint settings, the setup is per default locked. The transducer will reply with
error code “NAK180” if the user tries to change parameters. To change pre-configured parameters,
refer to the unlock procedure on page 23.
Setpoint setup by Serial interface
The correct procedure for setting up set point parameters are:
1. Enter set point value 5.00E-3 Torr
Command: @253SP1!5.00E-3;FF Reply: @253ACK5.00E-3;FF
2. Select set point direction (ABOVE/BELOW)
Command: @253SD1!BELOW;FF Reply: @253ACKBELOW;FF
3. Enter set point hysteresis value, if other than default +/- 10% of set point value is required.
Command: @253SH1!1.00E-2;FF Reply: @253ACK1.00E-2;FF
4. Enable set point
Command: @253EN1!ON;FF Reply: @253ACKON;FF
Setpoint setup by PDR900 Controller
1. Edit > Setpoint > Setp. Value 1
Enter set point value 5.00E-3 Torr
2. Edit > Setpoint > Direction 1
Select set point direction
3. Edit > Setpoint > Hysteresis 1
Enter set point hysteresis value
Only if other than default +/- 10% of set point value is required.
4. Edit > Setpoint > Enable 1
Enable set point
Setpoint value
The setpoint value is the pressure either below or above which the setpoint relay will be energized.
Setpoint hysteresis value
The hysteresis value is the pressure value at which the setpoint relay will be de-energized.
Setpoint direction
The setpoint direction determines whether the relay is energized above or below the set point value.
Enable setpoint
The enable setpoint enables or disables the set point.

The 925 transducer has an auto hysteresis setting of 10% of the set point value that
overwrites the current hysteresis value whenever the set point value or set point
direction is changed. If other hysteresis value than 10% is required, always set the set
point value and set point direction before setting hysteresis value.

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Setpoint safety delay (not available in EtherCAT units)
The setpoint safety delay function requires 5 continuously measurements that exceeds setpoint value before the
relay is tripped. This feature prevents false trigging of the setpoint relay due to noise. If fast setpoint response is
required the setpoint safety delay can be disabled.
Setpoint safety delay (not available in EtherCAT units)
Command: @253SPD!ON;FF
Command values: ON, OFF
Command reply: @253ACKON;FF
Query: @253SPD?;FF
Query reply: @253ACKON;FF
Factory default: ON
Integrated Touch Display (not available in EtherCAT units)
For 925 transducer versions with integrated touch display it is possible to see information about setpoints, sensors,
model, and measurements unit. A pressure threshold alarm can be set and for transmitters with multiple sensors, it
is possible to choose which sensor pressure value is displayed on the screen. All of this is accessible by the
following menu structure:

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Using the integrated touch display:
When the transducer is turned on, the initializing screen shows the transducer name while starting up. After start-
up, the screen automatically switches to the Main screen. To access the Menu, push anywhere on the Main screen.
The following table shows the different menus and options available:
Display-screen
Information
Start-up
MKS logo and transducer model
Home
The Home screen shows the current pressure, the transducer model, the status of the setpoints, the
triggering direction of each setpoint and shows if an alarm is enabled.
The setpoint buttons and unit text give quick access to the separate Setpoint-screens and Unit screen
respectively.
Menu
The general Menu contains 4 buttons which lead to:
Settings, Sensor, Setpoints menu and Home.
Settings
The Settings menu contains 4 buttons which lead to:
Model info, Setup menu, Unit and Back
Setup
The Setup menu contains 3 buttons which lead to:
Screen rotation, Alarm and Back
Sensor
The Sensor screen shows which sensor’s measurement is displayed on the Home screen
(green marked sensor).
Setpoints menu
The Setpoint menu contains 4 buttons which lead to:
Setpoint 1, Setpoint 2, Setpoint 3 and Back (to Menu)
Setpoint screen
Setpoint 1,2 or 3
Each Setpoint screen shows the setpoint status, the pressure unit, pressure triggering direction,
setpoint value and hysteresis value.
The setpoint status is indicated by:
X
Setpoint disabled (Grey)
ON
Setpoint enabled ON (Green)
OFF
Setpoint enabled OFF (Red)
If the Setpoint screen is accessed via the Setpoint menu, pressing the screen will lead back to the
same menu. If accessed via the quick-access buttons on the Main screen, pressing the screen will
lead back to the Main screen.
Model info
The Model info screen shows the transducer type and model number and each screen has different
extra information. Press the screen to toggle through the different info screens and eventually go back
to Settings.
Model info (1/4)
Model info (2/4)
Model info (3/4)
Model info (3/4)
Transducer P/N
Gas type
Interface type
User switch ON/OFF
Serial number
Transducer firmware
version
Connector type
Setpoint delay 50ms
ON/OFF
User tag
Display firmware
version
Number of available
relays
Relay communication
delay ON/OFF
Communication address
RS-485 testing
Temperature (°C)
Baud rate
Pressure unit
Transducer ON-time
Unit
The Unit screen displays the current pressure unit and gives the possibility to change the pressure
unit between Torr, Millibar or Pascal.
Screen rotation
The Screen Rotation screen displays the current screen orientation and enables the operator to rotate
the screen in four directions.
Alarm
A visual alarm can be set at a certain pressure.
Press the green or red button to enable or disable the alarm.
Press Set to change the alarm pressure value and triggering direction.
Set Alarm (1/2)
Setting pressure threshold:
The alarm value is set by selecting a digit (left and right arrow) and cycling through the numbers 0-9
and +/- (press up arrow or screen)
To accept, press right arrow until a green checkmark appears. Press again to proceed.
To cancel, press left arrow until a red arrow appears. Press again to proceed.
Set Alarm (2/2)
When the alarm is set, the operator selects whether the alarm triggers above or below the given value.

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Pressure output
The 925 transducer can provide pressure measurement output as an analog voltage value or RS-232/RS-485
digital value. The digital value is 3 digits scientific notation for PR1 reading and 4 digits for PR4 reading.
NOTE: For EtherCAT units, see the EtherCAT Communication Protocol instruction manual #20003335.
Pressure request:
Query: @253PR1?;FF
Query reply: @253ACK1.23E-4;FF
The analog output provides a 16 bit voltage output of 1VDC/ decade the standard configuration. Refer to Analog
out for details page 25.
When designing external pressure control loops make sure that external equipment like pumping
system is not damaged if the transducer output enters Sensor defect mode or in case of power
failure.
When designing pressure data collecting software and controlling loop make sure that the software
does not interpret a communication error as a valid pressure value.
Resolution
The digital pressure output can provide 3 digit or 4 digit values however, the resolution is limited in certain parts of
the measuring range.
1.00E-5 to 1.00E-4 Torr 1 digit resolution 1.000E-5
1.00E-4 to 1.00E-3 Torr 2 digit resolution 1.200E-4
1.00E-3 to 900 Torr 3 or 4 digit resolution 1.234E-3
Measuring noise
External sources can interfere with the sensor signal and cause noise on the signal. The low measuring range is
most sensitive to measuring noise due to low signal levels.

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Calibration and adjustment
The 925 is factory calibrated when delivered and in most applications further calibration is not required.
If the sensor element has been contaminated or damaged by process gases, adjustment of zero and full scale can
be executed to compensate for measurement errors.

The 925 is calibrated at the factory for reading Nitrogen gas. When exposed to
atmospheric air the transducer will read higher values typical 900 Torr at ambient
pressure.
Accuracy and repeatability
The 925 measuring accuracy is specified as transducer reading ± a percentage of the actual pressure. The basic
measuring accuracy is factory calibrated and cannot be user adjusted. The repeatability specification is the
transducers ability to repeat the same measurement value after multiple pressure cycles. Refer to the transducer
Specification page 57 for actual values.
Gas calibration
The 925 is based on measurement of thermal conductivity of the gas and consequently its reading depends on the
gas and gas concentration. The 925 is per default set to Nitrogen calibration, however the transducer has
calibration curves for several common gases.
NOTE: For EtherCAT units, see the EtherCAT Communication Protocol instruction manual #20003335.
Change of gas calibration setup:
Command: @253GT!ARGON;FF
Command values: NITROGEN, ARGON, HELIUM, HYDROGEN, H2O, NEON, CO2, XENON
Command reply: @253ACKARGON;FF
Query: @253GT?;FF
Query reply: @253ACKARGON;FF
Factory default: Nitrogen
Pressure unit calibration
The transducer can provide digital and analog output in Torr, mbar and Pascal pressure unit.
When changing unit all parameters like setpoint settings are automatically converted to the new unit, so it will
represent the same pressure level. All pressure parameters must be entered in the actual transducer unit setting.
NOTE: For EtherCAT units, see the EtherCAT Communication Protocol instruction manual #20003335.
Change of pressure unit calibration setup:
Command: @253U!PASCAL;FF
Command values: TORR, MBAR, PASCAL
Command reply: @253ACKPASCAL;FF
Query: @253U?;FF
Query reply: @253ACKTORR;FF
Factory default: TORR
The Torr unit is most common in the US and mbar is most common in Europe. Pascal is the official pressure unit as
specified by SI (from the French Le Système International d'Unités), and is widely used in Asia.
Zero Adjustment by serial interface
The zero adjustment function changes the measurement offset at low pressure. Temporally or permanent shift in
zero offset can be caused by contamination, corrosion, electrical noise interference and temperature.

Zero adjustment only changes the low measuring range and will have no influence on
measuring errors in the range from 1×10-2 and above.