Halma ALICAT SCIENTIFIC PCD User manual

OPERATING MANUAL
FOR DUALVALVE PRESSURE
CONTROLLERS
Models PCD · PCDS · PCD3 · IVCD

2 Introduction
Thank you for purchasing your pressure controller.
If you have any questions, or if something is not working as
expected, please contact us. We are eager to help you in any
way possible.
Contact Information
World Headquarters,
Tucson, Arizona, USA
[e-mail]
alicat.com
7641 N Business Park Dr.,
Tucson, AZ 85743 USA
[phone]
Europe
[email protected]om
Geograaf 24
6921 EW Duiven
The Netherlands
+31 (0)26 203.1651
China & SE Asia
[e-mail]
alicat.com.cn
2nd Floor, Block 63, No. 421,
Hong Cao Rd,
Shanghai 200233
PRC
[phone] ext. 801
India
[e-mail]
Halma India Pvt. Ltd.
Plot No . A-147, Road No. 24,
Next to Spraytech Circle
opp. Metropolitan Company,
Wagle Industrial Estate
Thane-West
Mahārāshtra 400 604
[phone]
Recalibrate your pressure controller every year.
Annual calibration is necessary to ensure the continued accuracy
of readings, and to extend the Limited Lifetime Warranty. Fill out the
Service Request Form at alicat.com/service,or contact us directly
when it is time to send in your device for recalibration.
For devices ordered with CSA, ATEX, ISO 17025, or other certifi-
cations, visit alicat.com/certifications for more information.
Serial #:
Next Calibration:
This device comes with a NIST-
traceable calibration certificate.
This device conforms to the European
Union’s Restriction of Use of Hazardous
Substances in Electrical and Electronic
Equipment (RoHS) Directive 2011/65/EU.
This device complies with the requirements
of the Low Voltage Directive 2014/35/EU
and the EMC Directive 2014/30/EU and
carries the CE Marking accordingly.
This device complies with the
requirements of the European Union’s
Waste Electrical & Electronic Equipment
(WEEE) Directive 2002/96/EC
DOC-MANUAL-PCD Rev 1, 2021.05.26
PCPDPSIDD
PCDPSIDD

2021.05.26  REV.   DUALVALVE PRESSURE CONTROLLER OPERATING MANUAL 3
Introduction
Your pressure controller has a variety of innovative features:
• 1000 readings per second guarantees high resolution
data, page 11.
• Backlit display with adjustable contrast is easy to read
even in direct sunlight. In dimly lit areas, press the logo
to turn on the backlight, page 17.
• Ability to control gases and liquids to accommodate
for a wide range of pressure control applications.
• Connection to a computer for control and data logging
to capture all pressure data for logging and
analysis, page 18.
This manual covers the
following instruments:
• PCD-Series: absolute, gauge, and
dierential pressure controllers for
closed volumes
• PCDS-Series: anti-corrosive
absolute, gauge, and dierential
pressure controllers for closed
volumes
• PCD3-Series: remote-sensing
pressure controllers for closed
volumes
• IVCD-Series: integrated
vacuum controllers for closed
volumes
• EXTSEN-Series: external
sensor pressure controllers for
closed volumes
For support or questions regarding
the use or operation of this device,
please contact us using the contact
information on page 2.
Alicat oers countless combinations of
device sizes, accessories, connections,
and configurations. These custom solutions
are offered to meet a variety of application
challenges brought forth by users pushing the
boundaries of our standard oerings.
If you have an idea for a new process or a challenging
application, contact Alicat for specialized engineering and
application support.
PCDPSIGD
PCRDPSIGD

4 Table of Contents
Contents
Introduction 3
Quick Start Guide 5
Getting Started 6
Getting to Know Your Pressure Controller 6
The Pressure Controller Display 6
Status Messages 6
Mounting 6
Filters 6
Device Ports 7
Connecting Your Pressure Controller 7
Applications 8
Gauge and Absolute Pressure Control 8
Remote-Sensing Pressure Control 8
Dierential Pressure Control 8
Dual-Valve Integrated Vacuum Controllers (IVCD) 9
Using Alicat Pressure Instruments with Liquids 9
Power and Signal Connections 10
Analog Signals 10
Displaying Live Data 11
Main Display 11
Taring Your Pressure Controller 11
How to Tare 11
When to Tare 11
Option: Color TFT Display 11
Control 12
Changing the Setpoint 12
Adjusting Setpoint with an IPC 12
Setpoint Setup 12
Using Autotare 12
Changing Between Setpoint Sources 12
Managing Setpoint with an Idle Modbus Connection 12
Managing Setpoint on Power-Up 12
Establishing Setpoint Limits 13
Control Loop 13
Changing the Controlled Variable 13
Adjusting the PD/PDF or PDI Control Algorithms 13
Tuning the PD/PDF Control Algorithm 13
Tuning the PDI Control Algorithm 13
Troubleshooting Valve Performance with PID Tuning 14
Using a Control Deadband for Pressure Control 14
Setpoint Ramping 14
Setting the Ramp Rate 14
Ramping Options 14
Displaying Valve Drive Percentage 15
Device Information 15
Setup 16
Sensor Setup 16
Choosing Engineering Units 16
Pressure Averaging 16
Zero Band 16
Configuring Serial Communications 16
Unit ID 16
Modbus RTU Configuration 16
Baud Rate 17
Display Setup 17
Main Screen Options 17
Screen Lighting 17
Display Rotation 17
Advanced Setup 17
Serial Communication 18
Modbus RTU Communication 18
Establishing Communication 18
Polling Mode 18
Streaming Mode 19
Taring 19
Collecting Data 19
Commanding a New Setpoint 20
Sending Setpoints as Floating Point Numbers 20
Quick Command Guide 20
Troubleshooting 21
General Use 21
Pressure Readings 21
Serial Communications 22
Maintenance 22
Cleaning 22
Recalibration 22
Reference Information 23
Engineering Units 23
Pinouts 24
8-Pin Mini-DIN (Default) 24
Locking Industrial Connector Pinout 24
9-Pin D-Sub Connector Pinouts 25
15-Pin D-Sub Connector Pinouts 25
M12 Connector Pinouts 26

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Quick Start Guide
Setup
Connect your pressure controller.
Choose your engineering units. You can
choose the measurement units by selecting MAIN
MENU →SETUP →Sensor →Engineering Units, see
page 16 for more details.
Operation: Pressure Verification
Monitor live pressure readings. Readings are
updated and displayed on your device in real
time. See page 11.
Connectors and Buttons
The drawing to the right represents a typical
configuration of a standard dual-valve pressure
controller. Your pressure controller’s appearance
and connections may differ. See page 2for
more examples.
Backlight
The monochrome display comes equipped with
a backlight. To toggle the backlight power,
press the logo on the front of your device.
For optional color TFT displays, pressing this
button will turn o the display to conserve power.
See page 11.
Maintenance and Care
Pressure controllers do not require cleaning
when flowing clean, dry gases. Read more on
page 22.
Calibrate your device annually. To schedule a
calibration, please contact support (page 2).
This is a typical
dual-valve gauge
pressure configuration.
This is a typical
dual-valve differential
pressure configuration.

6 Getting Started
Getting Started
Getting to Know Your Pressure Controller
The Pressure Controller Display
The figure below identifies the various features of the main pressure controller display.
Highlights pressure in the center of the display.
Tares the pressure (typically unavailable for abso-
lute pressure devices) (page 11).
Opens a menu to set the pressure control setpoint (page 12).
Enters the main menu system (page 11).
Toggles the backlight (more display options are on page 17).
✓ Note: Buttons 4 and 5 have no functions on the main display for pressure devices.
Status Messages
Status messages are shown to the right of the main readout number. In the example to
the right the LCK message indicates that the front display is locked.
ADC Analog-digital converter error
EXH Exhaust mode active
HLD Valve hold active
LCK Front display is locked
POV Pressure over range of device
Mounting
Pressure controllers do not require straight runs of pipe upstream or downstream. Most
pressure controllers can be mounted in any position, including upside-down. Corrosive-re-
sistant pressure controllers use media-isolated sensors that must be tared after changing
their orientation.
▲ Caution: Pressure controllers that use large Rolamite valves (PCRD, PCRD3, PCRDS)
should be mounted with their valve oriented vertically (right-side up). Please contact
Alicat for other orientations.
Filters
When pressure drop is not a concern, use in-line sintered filters to prevent large particulates
from entering the pressure controller. Suggested maximum particulate sizes are as follows:
• 20 microns for PCD, PCPD, PCHD, PCD3
• 40 microns for PCRD, PCRD3
The main display. Note the button
behind the logo, which toggles the
device backlight.
The main menu with valve position
information, and a LCK status.

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Device Ports
Your pressure controller has been shipped with plastic plugs fitted into its ports. To decrease
the chance of contaminating the flow stream, do not remove these plugs until you are ready
to install the device.
Standard pressure controllers have female inlet and outlet ports. VCR®-compatible and
other specialty fittings may have male connections.
• If you are using a fitting that does not have a face seal, use thread-sealing Teflon tape to
prevent leakage around the port threads, but do not wrap the first two threads. This
will minimize the possibility of getting tape into the flow stream.
• Face seal fittings do not need Teflon tape applied to the threads.
!
Warning: It is not recommended to use pipe dopes or sealants on the process connections
as these compounds can cause permanent damage to the controller should they get
into the flow stream.
Connecting Your Pressure Controller
Connect the controller so that the flow travels in the same direction as the flow arrow, usually
from left to right from the front of the device
! Warning: Using the pressure controller above the maximum specified common mode
or burst pressure will result in permanent damage to the internal pressure sensors.
Range Burst Pressure
Maximum Allowed Common Mode
Pressure (Differential Pressure Only)
0.07-100 PSI 3x full scale 200  (750  for anti-corrosive models)
500 PSI 1.5x full scale 750 
1000-3000 PSI 1.5x full scale N/A
A male VCR®-compatible
connection.
A default NPT female connection.
A male VCO®-compatible
connection.

8 Getting Started
Applications
Gauge and Absolute Pressure Control
The port on the face of the unit is connected to the closed volume where you want to control pressure. The valve on the
supply side will open to increase the pressure in the closed volume, and the valve on the exhaust side will open to
decrease pressure.
Remote-Sensing Pressure Control
PCD3-Series models sense and control the pressure at a point in the system outside of the pressure controller. An
additional NPT port on the back is connected directly to the absolute pressure sensor in the device. The pressure sensor
is isolated from the flow path in this configuration.
Dierential Pressure Control
PCD-PSID-Series pressure devices monitor and control the dierential pressure between two points in the system. These
devices have two ports located on the front face of the unit for connection to two points in the system where the
dierential pressure is measured from. The upstream port is for the higher of the two pressures, and the downstream
port is for the lower pressure. The process port is on the back of the unit. In these devices, the dierential pressure ports
have no flow, and are not connected to the flow path.
Gas Supply
or Atmosphere
Alicat
Controller
Pressure
Regulator
Flow in both directions
Closed Volume
at Setpoint Pressure
Exhaust to
Vacuum or
Atmosphere
Gas Supply
or Atmosphere
Alicat
Controller
Flow in both directions
Remote Sense Line (no flow)
Located behind the unit
Closed Volume
at Setpoint Pressure
Exhaust
Pressure
Regulator
Gas
Supply
Alicat
Controller
Flow
Exhaust
Process line
(port is in the back of the unit)
P1 Sensor (no flow)
P2 Sensor (no flow)
Process/Device under Test
P P2
Pressure
Regulator

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Dual-Valve Integrated Vacuum Controllers (IVCD)
IVCDs are similar to the PCD-Series absolute pressure controllers in functionality and in the navigation menus available
on the screen. IVC devices are used in applications where precise control of vacuum is required, and are available with
10 TorrA, 100 TorrA, 1000 TorrA, and combined 1000 & 10 Torr sensors.
Integration of the vacuum sensor, control valve, and PID algorithm in a single device eliminates the need for an external
vacuum sensor and throttle valve in your system. These devices have /-20 SAE ports, or optional VCR®-compatible,
compression, and VCO®-compatible fittings. Process port sizes may change depending on the valve on your device.
Using Alicat Pressure Instruments with Liquids
Many pressure devices may be used with chemically-compatible liquids, but a few warnings must be taken into account:
• Water is about 50 times more viscous than air. This is important when sizing a pressure controller, as this significant
increase in viscosity requires a larger valve to reach expected flow rates. For example, a PCD-series pressure controller
sized to flow up to 25  of air will be limited to roughly 0.5 LPM of water (or similar fluid).
• The factory PID tuning terms are established using air. It may be necessary to adjust the PID tuning parameters if you
will be using a controller with liquid. Find more information at alicat.com/PID, or contact us (page 2) to help you
through this tuning process.
▲Caution: Please check with Alicat before using your pressure controller with liquids unless specifically ordered
for this purpose.
Gas Supply
Alicat IVCD Optional Remote Sensor (on the back of IVC3 models)
Bidirectional Flow
Exhaust
Vacuum Pump Process

10 Getting Started
Power and Signal Connections
Power can be supplied to your controller through either the power jack or the multi-pin
connector on top of your device.
✓ Note: Power requirements vary based on analog configuration and valve type. Please
reference the associated specification sheet at alicat.com/specs for power requirements.
Standard 8-Pin Mini-DIN Pinout
Pin Function
Not Connected Optional: 4–20 mA primary output signal
Static 5.12 Vdc by default. Optional: secondary analog output
(4–20 mA, 0–5 Vdc, 1–5 Vdc, 0–10 Vdc) or basic alarm
Serial RS-232 RX / RS-485(−) Input Signal (receive)
Analog Setpoint Input
Serial RS-232 TX / RS-485(+) Output Signal (send)
0–5 Vdc Optional: 1–5 Vdc or 0–10 Vdc output signal
Power In (as described above)
Ground (common for power, digital communications, analog signals and alarms)
The above pinout is applicable to all devices with the Mini-DIN connector. The availability of dierent output
signals depends on the options ordered. Optional configurations are noted on the unit’s calibration sheet.
▲Caution: Do not connect power to pins 1 through 6, as permanent damage can occur.
It is common to mistake pin 2 (5.12 Vdc Output) as the standard 0–5 Vdc analog output
signal. Pin 2 is normally a constant 5.12 Vdc.
More pinout configuration options begin on (page 24).
Analog Signals
Primary Analog Output Signal
Most devices include a primary analog output signal, which is linear over its entire range.
For ranges that start at 0 Vdc, a zero-pressure condition is indicated at approximately 0.010
Vdc. Full scale pressure is indicated by the top of the range: 5 Vdc for 0–5 Vdc, 20 mA for
4–20 mA signals, and so on.
Option: Secondary Analog Output Signal
The default 8-pin Mini-DIN connector places the secondary analog output on pin 2 for both
voltage and current signals. Since pressure is the only measured parameter in the pressure
series, this secondary analog output can be used as a comparison to the primary analog
output.
Option: 4–20 mA Current Output Signal
If your controller has a primary or secondary output signal of 4–20 mA current, your pressure
controller will require 15–30 Vdc power.
▲
Caution: Do not connect 4–20 mA devices to “loop powered” systems, as this will
damage portions of the circuitry beyond repair and void the warranty. If you must
interface with existing loop powered systems, always use a signal isolator and a separate
power supply.
A dual-valve gauge pressure
controller with the standard 8-pin
Mini-DIN serial connector.
Male Connector: Cable
Female Connector: Device
1
4
5
68
7
3
2 1
4
5
6
87
3
2

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Displaying Live Data
Main Display
The main display has four primary functions:
• Displaying live pressure data
• Setting the pressure controller’s setpoint
• Taring the pressure (page 11)
• Accessing the main menu (MENU)
Live data is measured 1000 times per second and the LCD display is updated 10 times per
second. The button next to the measurement highlights its value in the center.
Taring Your Pressure Controller
MENU →TARE PRESS or TARES
Taring ensures your pressure controller provides its most accurate measurements. This
function gives the pressure controller a zero reference for pressure measurements.
How to Tare
MENU →TARES →TARE PRESS
• Tares should be tared with the pressure controller open to atmosphere with no flow.
• Absolute pressure devices can be tared if purchased with the optional internal barometer,
and then opened to atmosphere with no flow.
• Dierential pressure devices require zero dierential pressure between the P1 and P2
ports. They must be either open to atmosphere on both ports, or connected to the same
pressure source.
When to Tare
• Before every new pressure measurement cycle
• After significant changes in temperature or pressure
• After dropping or bumping the pressure controller
• After installing the controller in a dierent orientation
Option: Color TFT Display
Instruments ordered with a color display are functionally the same as standard backlit
monochrome instruments. The color enables additional on-screen information.
Multi-Color Display Indicators
• GREEN: Parameter labels and adjustments associated with the button directly above or
below the label are presented in green.
• WHITE: The color of each parameter will be displayed in white when the device is
operating within device specifications.
• RED: The color of a parameter will be displayed in red when its value exceeds 128% of
the device’s specifications.
• YELLOW: Menu items that are ready to be selected appear in yellow. This color replaces
the > symbol in selections on monochrome display.
✓
Note: Press the logo to turn o the color display backlight. The pressure controller
remains in operation while the backlight is o.
✓
Note: Color displays will require an additional 40 mA when using a 12 Vdc power supply.
All other device specifications from your device’s specification sheet remain in eect.
The main display. Note the button
behind the logo, which toggles the
device backlight.

12 Control
Control
Changing the Setpoint
SETPT or MENU →CONTROL →Setpt:
The setpoint selection screen indicates the engineering units and maximum allowable
setpoint (e.g., : +10.000 Max). To cancel a setpoint, press CLEAR, then SET.
Adjusting Setpoint with an IPC
For controllers ordered with a potentiometer control knob (IPC), the setpoint source must be set to analog for the controller
to receive setpoint commands from the IPC (see “Changing Between Setpoint Sources” below).
Leave the IPC knob at the midpoint when it is not in use.
Setpoint Setup
Using Autotare
CONTROL →Setpoint Setup →Zero Setpoint
When the setpoint is zero, the controller will automatically tare itself if autotare is enabled. This menu also specifies how
many seconds after a zero setpoint the controller will wait, under Delay Before Tare.
▲Caution: Auto-tare is typically not recommended for pressure control applications.
Setpoint ramping (page 14) can either be set to honor the ramp rate limit or to go to zero as quickly as possible.
Changing Between Setpoint Sources
CONTROL →Setpoint Setup →Setpoint Source
Pressure controllers with RS-232 or RS-485 communication will accept setpoints from the front panel and serial commands
(page 18), or from an analog signal.
• When the source is set to Serial/Front Panel , the controller will accept input from either the front panel, or an RS-232/
RS-485 connection. Neither source is a slave of the other, so the controller will accept the most recent command
from either source.
• When the source is set to Analog, the device ignores serial setpoint commands and will prevent setpoint input from
the front panel.
Managing Setpoint with an Idle Modbus Connection
CONTROL →Setpoint Setup →On Modbus Timeout
If a Modbus connection is idle for a specified amount of time, the device can be configured to set a zero setpoint, or
maintain the previous setpoint. The idle time will be infinite by default and can be adjusted (page 16).
Managing Setpoint on Power-Up
Power-Up Setpoint Value
CONTROL →Setpoint Setup →Power Up Setpoint →Value
By default, the controller remembers its last setpoint across power cycles. However, it can be changed to give a specified
setpoint upon power-up by selecting Fixed Setpoint and entering a value. If the setpoint will be digitally provided more
often than every few minutes, use a fixed setpoint on power-up to avoid wearing out non-volatile memory in the device.
Power-Up Setpoint with Ramping
CONTROL →Setpoint Setup →Power Up Setpoint →Ramp
Any setpoint ramp will always start from zero on power-up. Similar to the zero setpoint option (page 16), the device
can either honor the ramp rate (Honor from 0) or jump to setpoint (Jump from 0) as quickly as possible.
The control menu.

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Establishing Setpoint Limits
CONTROL →Setpoint Setup →Setpoint Limits
The setpoint limits menu configures upper and lower limits for selecting a pressure control setpoint. By default, the controller
will only be limited by its measuring range; however, more strict limits may be beneficial in certain critical applications.
Over a serial connection, requesting a setpoint outside the limit will be rejected and an error will be returned. When
using an analog setpoint signal, setpoints that are outside of the setpoint limits are treated as if they were at the nearest
limit. For example, if you request a setpoint that is below the lower limit, the controller sets the setpoint at the lower limit.
✓
Note: When changing from one control loop variable to another, the pressure controller remembers setpoint limits as
percentages of full scale. For example, a 15- limit on a 30- pressure controller (50% of full scale) will become a
limit of 50% if the control loop is changed to valve drive.
Control Loop
Changing the Controlled Variable
CONTROL →Control Loop →Control
Selectable control loop variables include pressure (absolute, gauge, or dierential) and valve drive.
✓
Note: Pressure controllers with upstream valves will control the outlet pressure. Those with downstream valves can control
upstream backpressure, but these must be configured for this type of control.
!
Warning: When changing the control loop, you may need to adjust the PID settings for optimal stability and speed of
response.
Adjusting the PD/PDF or PDI Control Algorithms
CONTROL →Control Loop →Loop Type
Your pressure controller uses an electronic closed loop controller to determine how to actuate its valve(s) in order to
achieve the commanded setpoint. These settings are tuned for your specific operating conditions, but changes to your
process sometimes require on-site adjustments to maintain optimal control performance. If you encounter issues with
control stability, oscillation, or speed of response, fine-tuning your closed loop control may help.
For most applications, the PD/PDF algorithm is recommended.
Tuning the PD/PDF Control Algorithm
The controller’s default control algorithm (PD) employs pseudo-derivative feedback (PDF) control, which uses two editable
variables:
• The larger the Dgain, the slower the controller will correct errors between the commanded setpoint and the measured
process value. This is equivalent to the P variable in common PDF controllers.
• The larger the Pgain, the faster the controller will correct for osets based on the size of the errors and the amount
of time they have occurred. This is equivalent to the I variable in common PDF controllers.
✓ Note: The D and P variables in the PD/PDF control algorithm are more typically referred to as P and I, respectively, in PDF
controllers.
Tuning the PDI Control Algorithm
The controller’s PD²I control algorithm (also called PDDI) is used to provide faster response, most commonly in dual-valve
flow and pressure controllers. This algorithm uses typical PI terms and adds a squared derivative term (D):
• The larger the Pgain, the more aggressively the controller will correct for errors between the commanded setpoint
and the measured process value.
• The larger the Igain, the faster the controller will correct for osets based on the size of the errors and the amount
of time they have occurred.
• The larger the Dgain, the faster the controller will predict necessary future corrections based on the current rate of
change in the system. This often results in slowing the system down to minimize overshoot and oscillations.

14 Control
Troubleshooting Valve Performance with PID Tuning
The following issues can often be resolved by adjusting the PID gain values for your pressure controller.
Fast oscillation around the setpoint
• PD: Reduce the Pgain in decrements of 10%.
• PD²I: Increase the Pgain in increments of 10%, and then adjust the Igain to fine-tune.
Overshot setpoint
• PD: Reduce the Pgain in decrements of 10%.
• PD²I: If Dis not , increase the Pgain in increments of 10%.
Delayed or unattained setpoint
• PD: Increase the Pgain in increments of 10%, and then decrease the Dgain by small amounts to fine-tune.
• PD²I: Increase the Pgain in increments of 10%, and then increase the Igain to fine-tune.
✓ Note: Valve tuning can be complex. More detailed information is available at alicat.com/pid.
Using a Control Deadband for Pressure Control
CONTROL →Control Loop →Control Deadband
The control deadband is designed to minimize the amount of gas exhausted and improve stability. There is no active
control within the deadband setting.
To turn on the control deadband, enter a non-zero value in CONTROL → Control Deadband → Deadband. In order for the
deadband to activate, the controller must reach the setpoint. If the process variable drifts outside a deadband limit, active
control resumes until the setpoint is reached again.
The controller can be set to either hold the current valve position or close the valve(s) in CONTROL → Control Loop →
Control Deadband → When in Band. It is recommended to close the valves on PCD-Series controllers.
Example: With a setpoint of 30 , a deadband of ±0.25  allows absolute pressure to vary between 29.75 and
30.25 . The device will increase pressure until it reaches the setpoint of 30 . With a setting of Close valve, it will
close both valves until the pressure reading varies outside of the preset deadband.
Setpoint Ramping
Setpoint ramping regulates how quickly the controller will reach the pressure setpoint. It is often used to prevent bursts
of flow from damaging delicate instruments when starting a process.
To activate setpoint ramping, set a maximum ramp rate and configure when to enable the ramping function.
Setting the Ramp Rate
• Ramp is a quick way to change the maximum rate of change.
• Units is a quick way to change the engineering units used.
• Set By Delta / Time allows for more detailed control of the ramp rate including changing the value of the time period
Ramping Options
Changing ramping options allows you to have a ramp in only one direction, increasing or decreasing. It also allows you
to ignore the ramp rate when initially powering on or commanding a zero setpoint.
• Ramp Up toggles on and o. When o, the ramp rate will not be honored when increasing pressure to reach a given setpoint.
• Ramp Down toggles on and o. When o, the ramp rate will not be honored when decreasing pressure to reach a given setpoint.
• Power Up toggles between Allow Ramp and No Ramp. If set to No Ramp, the device will ignore the ramp rate just after
powering on, otherwise it will honor the ramp rate from a zero setpoint.
• 0 Setpt determines whether the controller ramps when a zero setpoint has been given. If this setting is set to No
Ramp, when given a zero setpoint, the controller will immediately snap to the zero setpoint; otherwise it will ramp at
the selected rate.

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Displaying Valve Drive Percentage
The valve drive is represented as a percentage of the amount of voltage driven to the valve. Percentages do not directly
correlate with percentage open.
Viewing the valve drive percentage is particularly helpful for troubleshooting. An increasing percentage over time likely
indicates a clog in the system, where more voltage is required to drive the valve to attain the same amount of flow. A
valve percentage of 0% indicates the valve is closed.
This information may be displayed on the main display and/or as part of transmitted serial data. There are four valve
display options:
• None: No valve information is displayed.
• Main Screen: Only on the main display.
• Digital Data: Only in the serial data frame.
• Screen and Digital: Both the main display and serial data frame.
Device Information
The ABOUT menu (MENU →ABOUT) contains useful information for setup, configuration,
and troubleshooting.
Basic Device Information
ABOUT →About Device
This includes information on the following:
• MODEL: Device model
• SERIAL NO: Serial number
• DATE MFG: Manufacturing date
• DATE CAL: Most recent calibration date
• CAL BY: Initials of the person who calibrated the device
• SW: Firmware version
• Display SW (color displays only): Firmware version of the display
Device Full Scale Ranges
ABOUT →Full Scale Ranges
This displays the maximum calibrated range of available pressure readings. Most will include only one type of pressure.
Devices equipped with an optional barometer will show absolute, gauge, and barometric pressures.
Manufacturer Information
ABOUT →About Manufacturer
About Manufacturer usually includes:
• Manufacturer name
• Web address
• Phone number
• Email address
The setup menu.

16 Setup
Setup
Sensor Setup
MENU →SETUP →Sensor
Choosing Engineering Units
SETUP →Sensor →Engineering Units
Changing engineering units alters both the display and the data frame. Choose the parameter whose unit you want to
change, and then choose an engineering unit. Confirm the change on the last screen.
Pressure Averaging
SETUP →Sensor →Pressure Averaging
Averaging the pressure over a longer time may be useful in smoothing fluctuating readings. This menu changes the time
constant of the geometric running average for pressure. Values roughly correspond to the time constant (in milliseconds)
of the averaged values. Higher numbers generate a greater smoothing eect, to a maximum of 255 ms.
Zero Band
SETUP →Sensor →Zero Band
The zero band threshold is an amount of pressure under which pressure values are displayed as . The maximum zero
band is 6.38%. This function also applies to gauge pressure readings when using the optional barometer. For example,
a 20  controller with a zero band value of 0.25% would display all readings between -0.05 and 0.05  as  .
Configuring Serial Communications
MENU →SETUP →RS-232 Serial or RS-485 Serial
You can operate the pressure controller remotely via its data connection for easy streaming and logging of all data.
Before connecting the pressure controller to a computer, ensure that it is ready to communicate with your computer by
checking the options in this menu.
For more on how to issue commands from a computer, see page 18.
Unit ID
SETUP →RS-232 Serial or RS-485 Serial →Unit ID
The unit ID is the identifier that a computer uses to distinguish your device from other, similar devices when connected
to a network. Using the unit ID letters A–Z, you can connect up to 26 devices to a computer at the same time via a single
 port. This is called polling mode (page 18). Unit ID changes take eect when you select SET.
If you select “@” as the Unit ID, the pressure controller will enter streaming mode when you exit the menu (page 19).
Modbus RTU Configuration
SETUP →RS-232 Serial or RS-485 Serial →Modbus Address
SETUP →RS-232 Serial or RS-485 Serial →Modbus
Modbus Address
The Modbus address is the identifier that a computer or programmable logic computer (PLC) uses to distinguish your
device from other devices when connected to a Modbus network. Values of 1–247 are available for use.
Managing Setpoint with an Idle Modbus Connection
If a Modbus connection is idle for a specified amount of time, the device can be configured to set a zero setpoint, or
maintain the previous setpoint. The idle time will be infinite by default and can be set, in seconds, up to 99999.9 seconds
(1 day, 3 hours, 46 minutes, 39.9 seconds).
The setup menu.

2021.05.26  REV.   DUALVALVE PRESSURE CONTROLLER OPERATING MANUAL 17
Baud Rate
SETUP →RS-232 Serial or RS-485 Serial →Baud Rate
Baud rate is the speed at which digital devices transfer information. The pressure controller has a default baud rate of
19200 baud (bits per second). If your computer or software uses a dierent baud rate, you must change the pressure
controller’s baud rate in the BAUD menu to ensure they match. Alternatively, you can change your computer’s baud rate in
Windows® Device Manager. Baud rate changes take eect once you press SET, but you may need to restart the software
for it to recognize the change.
Display Setup
MENU →SETUP →Display
The options in the display setup menu adjust the contrast/brightness of the display and enable screen rotation.
Main Screen Options
SETUP →Display →MAIN Screen
• Any Key Press changes what happens when any of the parameter buttons on the main display (page 11) are
pressed (pressure or temperature, for example). By default, these buttons highlight their measurement in the center
of the display. If this option is set to Show Actions Menu, an option to change that parameter’s engineering units will
be shown, as well as an option to highlight the parameter.
• Show Valve Drive shows or hides the valve’s drive percentage. See page 15.
• Top Left Key Value and Bot Left Key Value will show if the device has an optional barometer installed. This option
configures which type of pressure (barometric, gauge, absolute) is displayed.
Screen Lighting
SETUP →Display →Screen Lighting
The options and wording in the screen lighting menu will vary for monochrome versus color displays.
• On monochrome displays, press LESS CONTRAST or MORE CONTRAST to adjust the contrast levels and move the contrast
indicator left or right. POWER UP Lit or Dark toggles whether the backlight of the unit will be on when the device
powers on.
• On color displays, press DIMMER or BRIGHTER to adjust the brightness level and move the brightness indicator left or right.
Display Rotation
SETUP →Display →Display Rotation
The device has the option of inverting (flipping) the screen upside-down, as configured in this menu.
Advanced Setup
MENU →SETUP →Advanced
The advanced setup menu contains settings and detailed information that are useful when troubleshooting with customer
support.
Factory Restore
SETUP →Advanced →Factory Restore
This will immediately take you to a confirmation screen. When troubleshooting, an applications engineer may recommend
doing a Factory Restore. If something is not acting as expected, please contact an applications engineer prior to doing
a Factory Restore.
Register Status
SETUP →Advanced →Register Status
The Register Status screen displays live values for the internal device registers. Many of these values can help an
applications engineer diagnose operational issues over the phone. Some register values clearly distinguish between
hardware and operational problems, which speeds up the troubleshooting process.
Edit Register and Device Properties
SETUP →Advanced →Edit Register and SETUP →Advanced →Device Properties
! Warning: Editing these settings may cause the device to become inoperable. Do not modify them without working with
an applications engineer.

18 Serial Communication
Serial Communication
Connecting your device to a computer allows you to log the data that it generates. The pressure controller communicates
digitally through its communications connector and cable using a real or virtual  port on your computer. This section
of the manual shows you how to operate the pressure controller using ASCII commands.
Modbus RTU Communication
For details on Modbus commands, please visit alicat.com/manuals for the Modbus operating bulletin.
Establishing Communication
After connecting your pressure controller using a communications cable, you will need to establish serial communications
through a real or virtual  port on your computer or programmable logic computer (PLC).
• If the device is connected to a serial port, note its  port number. This can be found in Windows® Device Manager.
• If you have used a USB cable to connect your device to your computer, then in most cases it will recognize your USB
as a virtual  port. If it does not, download the appropriateUSB device driver at alicat.com/drivers and note the
 port number as found inWindows® Device Manager.
The controller will be configured with the following settings:
• Baud: 19200 (by default; others can be used if the computer, its software, and the controller are all set to the same rate)
• Data bits: 8
• Parity: none
• Stop bits: 1
• Flow control: none
Alicat’s Serial Terminal Application
Alicat’s Serial Terminal is a preconfigured program for serial communications, functioning much like the older Windows®
HyperTerminal.
Download Serial Terminal for free at alicat.com/drivers. Once downloaded, simply run SerialTerminal.exe. Enter the 
port number to which your device is connected and the baud rate of the pressure controller. The default baud rate is
19200, but this is adjustable by entering the RS-232 Serial menu on your pressure controller (page 16).
✓
Note: In the following examples, indicates an ASCII carriage return (decimal 13, hexadecimal D). For many devices, this
is the same as hitting the Enter key. Serial commands are not case-sensitive.
Polling Mode
Your controller is shipped in polling mode with a unit ID of A, unless requested otherwise. Each poll returns one line of
data every time you request it. To poll, simply enter its unit ID.
Poll the device: [unit ID]
Example: a(polls unit A)
You can change the unit ID of a polling device by typing:
Change the unit ID: [current unit ID]@=[desired unit ID]
Example: a@=b(changes unit A to unit B)
You can also do this via the device’s front panel menu (page 16). Valid IDs are letters A–Z, and up to 26 devices may
be connected at a time, as long as each unit ID is unique.

2021.05.26  REV.   DUALVALVE PRESSURE CONTROLLER OPERATING MANUAL 19
Streaming Mode
In streaming mode, your device automatically sends a line of live data at regular intervals. Only one unit on a  port
may be in streaming mode at a time.
To put your pressure controller into streaming mode, type:
Begin streaming: [unit ID]@=@
Example: A@=@(Begins streaming unit A)
This is equivalent to changing the unit ID to “@”. To take the pressure controller out of streaming mode, assign it a unit
ID by typing:
Stop streaming: @@=[desired unit ID]
Example: @@=a(stops and assigns unit ID of A)
When sending a command in streaming mode, the flow of data will not stop while the user is typing. This may make the
commands you type unreadable. If the device does not receive a valid command, the command will be ignored. If in
doubt, simply hit and start again.
✓ Note: The default streaming interval is 50 ms, but this can be modified by editing Register 91 while the device is in polling
mode:
Set streaming interval: [unit ID]w91=[time in milliseconds]
Example: aw91=500(streams data every 500 ms)
Taring
Taring pressure ensures that the gauge or dierential pressure sensor reads zero. Taring an absolute pressure sensor
requires a barometer and aligns the absolute pressure sensor with the external barometric pressure. For an accurate
tare, a gauge or absolute pressure sensor must be open to atmosphere, while both ports of a dierential sensor must
be connected to the same pressure source (which may be atmosphere).
To tare a gauge or dierential pressure device:
Tare gauge pressure: [unit ID]p
Example: ap
To tare an absolute pressure device
Tare absolute pressure: [unit ID]pc
Example: apc
Absolute pressure devices will return a ?if the device is not configured with an internal barometer.
Collecting Data
Collect live data by typing the [unit ID]command or by setting your pressure controller to streaming. Each line of data
for live measurements appears in the format below, but the unit ID is not present in streaming mode.
Example:
A +20.00 +20.00
ID Gauge Pressure Setpoint
Single spaces separate each parameter, and each value is displayed in the chosen device engineering units (page 16).
You can query the engineering units of the serial data frame by typing:
Query live data info: [unit ID]??d*
Example: a??d*(returns the data frame descriptions)
Additional columns, including status codes (page 6), may be present after the last number. The unit ID appears in
the data frame only when the device is in polling mode.

20 Serial Communication
Commanding a New Setpoint
Before attempting to send a setpoint to your controller serially, confirm that its setpoint source is set to Serial/Front Panel
(page 12). There are two ways to command a new setpoint over a serial connection, as described below. In either of
these methods, the data frame returns the new setpoint value when it has been accepted as a valid setpoint.
Sending Setpoints as Floating Point Numbers
This is how to send the desired setpoint value as a floating point number in the selected engineering units:
New setpoint: [unit ID]s[floating point number setpoint]
Example: as5.44(setpoint of +5.44 PSIG)
When using a pressure controller configured to control negative pressure, negative setpoints are sent by adding a hyphen
for the minus sign (-):
New setpoint: [unit ID]s[floating point number setpoint]
Example: as-15.00(setpoint of −15.00 PSIG)
Quick Command Guide
✓ Note: Serial commands are not case-sensitive. In these examples, the unit ID of the controller is a.
Change unit ID: [current unit ID]@=[desired unit ID]
Tare pressure (PSID/PSIG): ap
Tare absolute pressure: apc(requires optional barometer)
Poll the live data frame: a
Begin streaming data: a@=@
Stop streaming data: @@=[desired unit ID]
Set streaming interval: aw91=[number of milliseconds]
New setpoint: as[setpoint as floating point #]
New setpoint: a[setpoint as integer where 64000 is full scale]
Hold valve(s) at current position: ahp
Hold valve(s) closed: ahc
Cancel valve hold: ac
Query live data info: a??d*
Manufacturer info: a??m*
Firmware version: a??m9
Lock the front display: al
Unlock front display: au
More information can be found on our online Serial Primer document, at alicat.com/drivers. If you require more advanced
serial communication commands, please contact support (page 2).