Teledyne DAVC-4 User manual

Digital AVC
INSTRUCTION MANUAL
(DAVC-4, DAVC-5, DAVC-6)
www.teledyne-hi.com
ISO 9001
CERTIFIED

174-012021_Digital AVC Page 2 of 23
Manual Print History
The print history shown below lists the printing dates of all revisions and addenda created for this
manual. The revision level letter increases alphabetically as the manual undergoes subsequent
updates. Each new revision includes a revised copy of this print history page.
Revision A (Document Number 174-062009) .......................................................................June 2009
Revision B (Document Number 174-072009) ........................................................................July 2009
Revision C (Document Number 174-072009)........................................................................July 2009
Revision D (Document Number 174-062010).......................................................................June 2010
Revision E (Document Number 174-082010) ...................................................................August 2010
Revision F (Document Number 174-112014) ............................................................. November 2014
Revision G (Document Number 174-072015)........................................................................July 2015
Revision H (Document Number 174-052016).......................................................................May 2016
Revision J (Document Number 174-012021) ................................................................... January 2021
Visit www.teledyne-hi.com for WEEE disposal guidance.
Hastings Instruments reserves the right to change or modify the design of its equipment
without any obligation to provide notification of change or intent to change.

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Table of Contents
1.0 GENERAL INFORMATION ........................................................................................................................................4
1.1 FEATURES ...............................................................................................................................................4
1.2 SAFETY ...................................................................................................................................................4
1.3 COMPLIANCE DATA ................................................................................................................................4
1.4 SPECIFICATIONS ......................................................................................................................................5
1.5 THERMAL COEFFICIENT..........................................................................................................................5
1.6 ACCESSORIES ..........................................................................................................................................6
2.0 INSTALLATION ............................................................................................................................................................9
2.1 POWER-I/O CABLE ..................................................................................................................................9
2.2 POWER REQUIREMENTS &PIN OUT.........................................................................................................9
2.3 SERIAL COMMUNICATIONS PIN OUT .......................................................................................................9
2.4 LINEAR OUTPUT PIN OUT.......................................................................................................................9
2.5 NON-LINEAR OUTPUT PIN OUT..............................................................................................................9
2.6 PRESSURE ALARMS PIN OUT .................................................................................................................10
3.0 VACUUM GAUGE OPERATION .............................................................................................................................11
3.1 QUICK START .......................................................................................................................................11
3.2 SETTING PRESSURE UNITS OF MEASURE ...............................................................................................11
3.3 NON-LINEAR ANALOG PRESSURE MEASUREMENT.................................................................................12
3.4 LINEAR ANALOG PRESSURE MEASUREMENT .........................................................................................14
3.5 ALARM SET POINT.................................................................................................................................17
3.6 DIGITAL COMMUNICATIONS.................................................................................................................18
3.7 OPERATION AND PERFORMANCE ...........................................................................................................20
3.8 GAUGE TUBE OPERATING PRINCIPLE....................................................................................................20
3.9 CALIBRATION PROCEDURE....................................................................................................................21
4.0 WARRANTY ................................................................................................................................................................23
4.1 WARRANTY REPAIR POLICY ..................................................................................................................23
4.2 NON-WARRANTY REPAIR POLICY .........................................................................................................23

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This manual contains technical and general information relating to the installation, operation, and
calibration of vacuum gauges and gauge tubes manufactured by Teledyne Hastings Instruments (THI).
For best performance, THI vacuum gauges should be operated with the appropriate THI gauge tube.
Attempting to use a THI vacuum gauge with another manufacturer’s tubes may result in damage to both
the gauge and tube.
1.1 Features
The THI Digital AVC (DAVC) is a digital readout version of THI’s AVC vacuum gauge. The heated gauge
tube supplies an analog, non-linear signal that is amplified for a zero to one-volt signal output. A precision
A/D converter, in conjunction with a microprocessor, measures the gauge tube’s signal output, converts
the measurement to a pressure reading using the gauge tube’s well defined output/pressure function, and
then provides the result to the end user through a serial communications port. In addition, the same
signal is converted to a linear analog output that is range selectable by the user.
The DAVC is available for use with three of THI’s most popular gauge tube families: The DV-6, DV-5, and
DV-4. The DV-6 range is 1.0 - 1000 mTorr. The DV-5 range is 0.1 – 100 mTorr. The DV-4 range is 0.2 –
20 Torr. All gauge-tubes used with the Digital AVC feature long life and minimal maintenance due to the
use of rugged, noble-metal, thermocouple (TC) gauge tubes that are designed specifically for each range.
1.2 Safety
The following symbols and terms may be found on THI products and/or in THI manuals and indicate
important information.
When found on the device, this symbol indicates that the operator should refer to the manual
for important instructions on the proper use of this device. When found in a manual, this symbol
indicates that the reader should understand the implications contained in the text before
operating the device.
The WARNING label indicates important information that should be heeded for safe and proper
performance of the device.
The label, CAUTION, is used to indicate that damage to the power supply or equipment connected to it,
could occur if directions are not followed. Warranty could be invalidated if the instructions in this manual
are not followed.
1.3 Compliance Data
1.0 General Information
CE Standard Compliance
Test Standard
SAFETY EN61010
EMC/EMI Family EN61326
CONDUCTED/RADIATED EN55011
ESD EN61000-4-2
RF EN61000-4-3
CONDUCTED IMMUNITY EN61000-4-6

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1.4 Specifications
Input Power ...............................................................................................................................11 – 32 VDC
.......................................................................................................................................................0.7 Watts
Cable .................................................................Combination power and RS232 cable, 1.5 meters, included
..........................................................................For CE Compliance, cable should never exceed 3.0 meters
Weight (Approx.) ........................................................................... 0.27 lbs (123 Grams) W/O Tube & Cable
Height (Length)........................................................................................................ 2.6”, W/O Tube & Cable
Width / Depth ........................................................................................................................................1.75”
Operating temperature Range ................................................................................................-20°C to 70°C
Standard Metal Gauge Tube...................................................................................(DV-6R, DV-5M, DV-4R):
Overpressure (Gauge tubes) .....................................................................................................50 psig max.
Material of Construction........................................................................................DAVC Housing: Aluminum
................................................................................................................Thermocouple: Glass, Noble Metal
Connections............................................................................................. High Density, 15-Pin, D Connector
............................................................................................................ Octal Tube Socket for Thermocouple
Alarms ................................................................................................................................. 0.50 Amps max.
Tube Leak Test...........................................................................................................<1x10-8 atm cc/sec He
Accuracy..................................................................... DV4, 0.02 – 20 Torr, ± (20% of Reading + 0.01 Torr)
Accuracy................................................................... DV5, 0.1 – 100 mTorr, ± (20% of reading + 0.2 mTorr)
Accuracy...............................................................DV6, 0.001 – 1.0 Torr, ± (15% of Reading + 0.001 mTorr)
Non-Linear Analog Output ............................................................................................................... 0-1 VDC
Linear Analog Output ...................................................................0-1, 0-5, 0-10, VDC and 0-20mA, 4-20mA
Digital Output............................................................ RS232 (9600 / 19.2k baud) (6-pin modular connector)
AC Tube Drive ....................................................................... 0.3 – 0.4 VAC, true RMS, 1 kHz square wave
AC Tube Drive ..................................................................... (Compatible with DV-4, DV-5, and DV-6 tubes)
Tube Input .................................................... 0 – 10 mVDC, (compatible with DV-4, DV-5, and DV-6 tubes)
Single Set Point Output............................................................... Open-collector transistor for over set point
Single Set Point
See tube Product Bulletin for available tube connection configurations.
1.5 Thermal Coefficient
The DAVC generates an AC voltage using an internal transformer. This heating voltage is supplied to
the vacuum tube to warm up the thermocouples in order to measure the pressure. As the ambient
temperature increases or decreases, the internal resistance of the copper winding in the transformer
also changes. This resistance change will change the AC heating voltage that the vacuum tube
receives. It will also change the pressure reading slightly. The typical rate of change for a given tube
type is given below:
DV6 0.2 mTorr/°C + 0.25% of reading/°C
DV5 0.08 mTorr/°C + 0.16% of reading/°C
DV4 2.6 mTorr/°C + 0.1% of reading/°C

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Increasing the temperature will cause the pressure readings to increase, while decreasing temperature
will cause the pressure readings to decrease. The instruments are initially adjusted at an ambient
temperature of approximately 22°C. This effect can be corrected by adjusting the low pressure reading at
the operating ambient temperature. The specified rate of change does not include any changes due to
thermal effects on the vacuum tube or actual changes in pressure that occur in a vacuum system during
temperature excursions.
1.6 Accessories
1.6.1 Installation Accessories
THI offers a complete line of system attachments that permit easy maintenance for contaminated
operations. Gauge tubes are offered with various system fittings to match almost any system
requirement. Additionally, THI’s complete line of quick disconnect attachments allows customers to install
these special fittings and easily replace sensors without vacuum sealant or Teflon® tape. For particularly
dirty systems, Hastings offers a particle dropout trap containing a series of nine separate baffles which
prevent solid contaminants from having a direct path to the sensor’s thermopile.
1.6.2 DV-6S: New DV-6 tube For Severe Environments
Hastings Instruments has developed a new gauge tube, the DV-6S, which is specifically designed for
outdoor use on cryogenic tanks including railcar and tanker truck applications. In addition to the DAVC,
the gauge tube is compatible with the hand-held HPM-4/6 and the analog VT-6.
The DV-6S is supplied with a protective cap. The O-ring-sealed cap protects the gauge tube pins from
moisture thus significantly reducing corrosion. A metal lanyard prevents cap loss. The tube is provided
with a standard 1/8” NPT fitting; however special fitting requests can often be met.
1.6.3 Calibration Reference Tubes
THI Reference Tubes employ the same metal thermopiles used in all THI Vacuum Gauge Tubes. The
thermopile is sealed in a glass capsule that has been evacuated, baked, outgassed, and then aged to
ensure long-term stability. The sealed capsule is then housed in a protective metal shell to provide a
rugged, trouble-free assembly.
Once assembled, the reference gauge tube is accurately calibrated to precisely simulate a gauge tube at
a given operating pressure. It provides quick and easy instrument re-calibration by merely plugging the
instrument and, in the case of the DAVC, adjusting the HTR potentiometer until the display reads the
exact pressure noted on the reference tube.
Reference Tubes for use with DAVC
55-104
DB-20
Ref Tube (DV-6) for DAVC-6 Calibration
55-101
DB-16D
Ref Tube (DV-4D) for DAVC-4 Calibration
55-103
DB-18
Ref Tube (DV-5) for DAVC-5 Calibration

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1.6.4 Tube Types and Cables
Extension Cables for VT Series (DAVC)
55-3 OM-8-OFV 8 Ft Extension Cable
55-22
OM-12-OFV
12 Ft Extension Cable
65-53 OM-25-OFV 25 Ft Extension Cable
65-102 OM-50-OFV 50 Ft Extension Cable
55-142 OM-100-OFV 100 Ft Extension Cable
Vacuum Gauge Tubes 1000 mTorr Range
Stock #
Model #
Description
55-38 DV-6M
1/8” NPT Standard (Yellow base)
55-38R DV-6R
1/8” Ruggedized
55-38RS DV-6
1/8” NPT Rohs
Rugged
55-38S
DV-6S
1/8” NPT Rugged/Vibration
55-251 DV-6-KF-16
KF
-16TM
55-267 DV-6-KF-25
KF
-25TM
55-283
DV-6-VCR
VCRTM
55-38R-CF DV-6R-CF
Mini Conflat
TM
Vacuum Gauge Tubes 100 mTorr Range
55-19
DV-5M
1/8” NPT (Red Base)
55-230
DV-5M -VCR
VCRTM
Vacuum Gauge Tubes 20Torr Range
55-19
DV-4D
1/8” NPT (Purple Base)
55-19R
DV-4R
1/8” NPT Ruggedized
55-258
DV-4D-KF-16
KF-16TM
55-266
DV-4D-KF-25
KF-25TM
55-227
DV-4D-VCR
VCR
TM

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1.6.5 Outline Drawing

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2.1 Power-I/O Cable
The Power-I/O Cable is assembled at the factory as shown in Fig. 1. Its terminal end is finished with
stripped wire ends each tinned with lead free solder. This configuration is consistent with the previous,
analog version of the AVC and its color-coded wire assignment remains the same, as much as possible,
considering the additional features of the Digital version.
2.2 Power Requirements & Pin Out
Supply the DAVC with a well regulated, 11 to 32 VDC power source capable of providing at least 0.7.
Watts between Power Common pin 4 (blue/-) and Power pin 3 (green/+). See Fig. 1.
2.3 Serial Communications Pin Out
The transmit line of the DAVC, RS232 TX pin 15 (pink), must be connected to the receive pin of the serial
connector on the computer and the receive line, RS232 RX pin 14 (tan) must be connected to the
transmit pin of the serial connector on the computer. A third line, Digital Common, pin 8 (black), should
join the common pins on both the computer and the DAVC.
RS-232 communication may be established with baud rates of 9600 or 19200 only. The communication
conditions of the DAVC are fixed at 8 data bits, 1 stop bit, no parity and no handshaking. See the
SERIAL COMMUNICATIONS subsection under OPERATION for the command set.
2.4 Linear Output Pin Out
A linear analog signal output line, pin 11 (red), can be configured to supply the following ranges:
0-20 mA, 4-20 mA, 0-1 VDC, 0-5 VDC and 0-10 VDC. The range is selected by sending an RS 232
Output Select command found in section 3.4.3 and then following the DAC Calibration instructions in
section 3.7.
2.5 Non-Linear Output Pin Out
A non-linear analog signal output line, pin 7 (yellow) supplies only a 0 to 1 VDC signal corresponding to
the output range of the selected tube. This signal should be measured with respect to the Analog Signal
Common at pin 6 (violet). See the Pressure vs. Analog Output Curve that follows in Section 3.3.
2.0 Installation

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2.6 Pressure Alarms Pin Out
A single pressure set point controls two open collector circuits. Alarm 1, the over-pressure condition is
available through pin 1 (gray) and Alarm 2, the under-pressure condition available through pin 2 (brown).
The open-collector circuits will need to be supplied with power and current limiting resistance by the end
user.
The circuit example illustrated in Figure 2 is limited to the voltage limitations of the DAVC. The maximum
continuous current should be limited to no more than 0.5 amps to avoid damage to the DAVC. The end
user must consider the 0.7-watt requirement of the DAVC as well as the additional power requirements of
their added load(s).
The alarm transistors consist of two BCW66HTA’s. Should the end user elect to use separate power
sources for the DAVC and the relay circuit, they should consider that the maximum collector-emitter
voltage is 45VDC and the maximum continuous current should be limited to no more than 0.5 amps to
avoid damage to the DAVC.

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All THI gauge tubes are shipped with a protective cap or cover at the evacuation port to reduce
contamination and prevent damage to the internal thermopile elements. Once the protective cap or cover
is removed, a tube can be installed in any convenient position in the vacuum system without adversely
affecting calibration or performance. The recommended orientation is with the tube vertical and its stem
down. This will aide in preventing condensable materials from remaining in the gauge tube.
3.1 Quick Start
1. Install the appropriate DV4, DV5 or DV6 gauge tube (See the bottom of the instrument to
determine the appropriate tube) into the vacuum system. When installing the gage tube, consider
the position of the keyed octal plug so that the LED’s and controls on the DAVC will be readily
accessible
2. Plug the gauge tube into the octal socket on the bottom of the Digital AVC.
3. Connect power common (-) to the blue wire (pin 4) and from +11 VDC to +32 VDC supply to the
green wire (pin 3). One of the LED's indicating over-pressure or under-pressure on the top of the
DAVC will illuminate.
4. While at one atmosphere, press the ATM button and release to set the atmosphere tube output for
this individual tube. The LEDS will flash while the button is pressed. Holding the button longer
than 3 seconds will reset the adjustment back to the default value.
5. The low pressure accuracy can be improved if the vacuum chamber can be pumped down below
the minimum pressure range of the attached tube can be reached, adjust the HTR potentiometer
until that pressure reading is reported (See the serial communication section) or until the analog
Pressure Signal Output, pin 7 (yellow) equals approximately 1.0 volts. Refer to Section 3.7 for
more information about tube calibration.
3.2 Setting Pressure Units of Measure
The DAVC comes factory configured for one of 3 possible pressure unit settings: Torr, mbar, or
Pascal. When setup at the factory, the configuration is laser etched into the housing. However, it can
be changed in the field using the RS-232 serial interface. If changed in the field, the units shown on
the DAVC will not match the units being reported when polled by a computer using the P<CR>
command. The pressure indication received serially will always report in the base of the selected units
using scientific notation.
To change the value reported by the DAVC to the desired unit of measure (UoM), send the U
command associated with that UoM. When changed, the analog output will be in the chosen UoM
despite that which is etched in the housing.
3.0 Vacuum Gauge Operation
Pressure Units RS232 Command
Torr U1<CR>
Pascal U2<CR>
mbar U3<CR>

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3.3 Non-Linear Analog Pressure Measurement
A non-linear, analog signal output line, pin 7 (yellow), supplies a 0 to 1 VDC signal corresponding to the
output range of the selected tube. This signal should be measured with respect to the Analog Signal
Common line, pin 6 (violet). See the INSTALLATION section for a diagram showing the Analog Signal
pin out.
This signal is equal to an amplified tube millivolt signal. This signal will NOT be linearly proportional to the
indicated pressure. One volt (1.2 V for DAVC4-1.2V) will correspond to a system pressure that is at least
one order of magnitude less than the minimum detectable pressure. Increasing pressure will be indicated
by a decreasing voltage as shown in the Analog Output vs. Pressure graph below. The minimum
detectable pressure is 0.1 millitorr for DAVC-5, 1 millitorr for DAVC-6 and 20 millitorr for DAVC-4.
The voltage signal, illustrated in the Analog Output vs. Pressure graph below, can be mapped to a
pressure value by using the following equation.
Where: V = Voltage and P = pressure in Torr for DV4 & DV5 versions and millitorr for DV6.
Parameters
DV6
DV5
DV4
DAVC-4-1.2V
a
-1623.22
-0.25948
-5.10184
-3.8115614
b
-58.0442
-42.23869
-6.91233
-2.5905928
c
-11732.2
-2.92598
-4.4943
-26.238798
d
-130.397
-256.99510
-6.30995
-22.881611
e
13338.17
3.18016
9.563177
24.483441
2
2
1dVbV
eVcVa
P++
++
=

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Analog Output vs Pressure
0.0001
0.001
0.01
0.1
1
10
100
00.2 0.4 0.6 0.8 11.2
Voltage
Pressure (Torr)
DAVC6
DAVC4
DAVC4-1.2V
DAVC5

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3.4 Linear Analog Pressure Measurement
A second analog signal output line, pin 11 (red), supplies one of five different ranges of linear signals
corresponding to the output range of the selected tube. This signal should be measured with respect to
the Analog Signal Common line, pin 6 (violet). See the INSTALLATION section for a diagram showing the
Analog Signal pin out.
The linear analog output of the DAVC provides voltage ranges of 0 – 1V, 0 – 5V, 0 – 10V. In addition, the
linear DAVC provides for 0-20mA, and 4mA - 20mA current ranges. This signal is equal to an amplified
tube millivolt signal. The TC transducer’s (the gauge tube) signals are linearly proportional to their
indicated voltage or current levels. Increasing pressure will be indicated by an increasing voltage or
current signal.
The pressure value can be mapped to the voltage signal by using the following equation.
Where:
V = Voltage signal,
P = pressure in Torr for DV-4, and in mTorr for DV-5, DV-6, and DV-33
PMAX = Max pressure range (20 Torr, 100 mTorr, 1000 mTorr)
VSPAN = Span Value in volts (example: 5 for 0-5v)








=
SPAN
MAX
V
P
VP

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The 4-20mA value can be mapped to a milliamp signal by using the following equation.
Where:
I = current in milliamps,
P = pressure in Torr for DV-4, mTorr for DV-5, DV-6, and DV-33,
PMAX = max pressure range (20 Torr, 100 mTorr, 1000 mTorr),
ISPAN = span value in milliamps (example: 20 for 0-20 mA, 16 for 4-20 mA),








=
SPAN
MAX
ZERO I
P
Ib
and
IZERO = the current corresponding to minimum pressure (zero).
i.e. 0 for 0-20mA and 4 for 4-20 mA range.
b
I
P
IP
SPAN
MAX
−








=

174-012021_Digital AVC Page 16 of 23

174-012021_Digital AVC Page 17 of 23
3.5 Alarm Set point
A single set point controls two open collector circuits.
Though not mechanical relays, the two circuits called Alarm
1 (P > SP) and Alarm 2 (P < SP) allow physical monitoring of
the state of the vacuum with respect to the set point.
Alarm 1 (P ˃SP), pin #1 (gray), is active when the red
LED is ‘ON’ indicating that the pressure is at or above
the set point.
Alarm 2 (P ≤SP), Pin #2 (brown), is active when the
green LED is ‘ON’ indicating that the pressure is below
the set point.
The open-collector circuits need to be supplied with their own power and current limiting resistance by the
end user. The load, controlled by the Open-Collector circuits, must not require voltages higher than those
specified for the DAVC (11 – 32 VDC) and must not exceed 500 mA of continuous current. See the
section on Pressure Alarms Pin Out for wiring instructions.
The alarm set point may be set in one of two ways:
One, by the measuring the Voltage signal between Analog Signal Common, Pin #6 (violet) and Setpoint
Level, Pin #5 (white) and setting the voltage using the SP potentiometer until the voltage corresponds to
the pressure indicated on one of the Pressure vs. Voltage charts above.
Two, by using the A2 command to send the set point voltage to the A/D converter in conjunction with a
P1 command to enable streaming while the pot is set to the desired trigger value. Remember to disable
streaming by issuing a P0 command and reset the signal source of the A/D converter by issuing an A0
command.
While the SP potentiometer is enabled using the PE command, the value of the set point is read
approximately every thirty seconds and compared to its previous setting. If the setting has changed, the
new setting will be stored to non-volatile memory. If the SP potentiometer is disabled using the PD
command, then no tweaking of the SP potentiometer will have any affect.
In either Enabled (PE) or Disabled (PD) cases, using the S1={m.dd}E{+e}<CR> command will re-write a
new set point. Only if the Potentiometer is enabled using the PE command, will adjustment of the
potentiometer affect a previous set point.

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3.6 Digital Communications
See the section on Serial Communications Pin Out for wiring instructions. RS-232 communication may be
established with baud rates of 9600 or 19200 only. The communication parameters of the DAVC are fixed
at 8 data bits, 1 stop bit, no parity and no handshaking. The command set can be found in the table
below. Communication with the serial interface of the Digital AVC is via an ASCII data string. The
command message consists only of a command string and the terminator. If all components of the ASCII
data string are valid the command will be accepted and executed.
3.6.1 Command Syntax
The following examples of syntax codes use special characters. The special characters are explained
below.
The first characters in each row of the format column represent a command string, either upper- or
lower-case command characters are accepted. All characters must follow each other in the string with
no spaces or other characters.
The characters within wavy brackets { } contain choices for the appropriate command.
The characters within the symbols < > are the common abbreviations for the one-digit ASCII control
codes which they represent, (e.g. <CR> represents carriage return).
All command strings must be followed by the terminator character (carriage return <CR>, also known
as ENTER).
When a lower-case character is present in an example it represents an option.
Character Description Valid Inputs:
m Most Significant Digit of Mantissa 1 - 9
d Decimal Digit 0 - 9
e Exponent 0 - 5
<CR> Command Terminator (carriage return) N/A
3.6.2 Interrogation Commands
Command Description Format Sample Response
Get Device ID ID<CR> Digital AVC<CR>
Get Current Pressure if A0 is set, P<CR> Pa: 1.23456e+0 Torr<CR>
Get Current Set Point if A2 is set,
Get Current heater potentiometer setting if A3 is set.
Get Relay Status RS<CR> 1,R1:ON<CR>
Get Setpoint S1<CR> SP1: 1.0240e-2 mbar<CR>
Get Serial Number (10-character max) SN<CR> 1023400012<CR>
Get Sensor Type ST<CR> DV-6<CR>
Get Raw Average Output Voltage – No Offset. U<CR> Vavg: 1.23456e-1 Volts<CR>
Get User Data (10-character max) UD<CR> TextString<CR>
Get Software Version # V<CR> Digital CVT 1.1.0 <CR>
Read DAC Zero Value DZ<CR> 2.564E04
Read DAC Span Value DS<CR> 2.983E04

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3.6.3 Parameter Modification Commands
Command Description Format Response notes:
Select 0-20 mA Linear Output D0<CR> OK
Select 1 Volt Linear Output D1<CR> OK
Select 4–20 mA Linear Output D4<CR> OK
Select 5 Volt Linear Output D5<CR> OK
Select 10 Volt Linear Output D10<CR> OK
Select A/D input 0 A0<CR> none Read from gauge tube
Select A/D input 1 A2<CR> none Read from Setpoint
potentiometer
Select A/D input 2 A3<CR> none Read heater adjust
potentiometer
Data streaming/Logging Off P0<CR> none Stops streaming output
Data streaming/Logging On P1<CR> See P cmd Reports signal Voltage and
pressure
Disable set-point pot. PD<CR> OK Lock out local setpoint
adjustment
Enable set-point pot. PE<CR> OK Enable local setpoint
adjustment
Modify Setpoint S1={m.dd}E{+e}<CR> OK 1.00000e-9 to 9.99999e+9
Set units to Torr U1<CR> OK All subsequent values in Torr
Set units to Pascal U2<CR> OK All subsequent values in Pascal
Set units to mbar U3<CR> OK All subsequent values in mbar
Modify User Data UD=TextString<CR> 10 character maximum
Send DAC Span Value DAS<CR> OK See section 3.8.2
to Linear Output
Send DAC Zero Value DAZ<CR> OK See section 3.8.2
to Linear Output
Send DAC Presure Value DAP<CR> OK See section 3.8.2
to Linear Output
Replace DAC Zero Value DZ={m.dd}E{+e}<CR> OK 1.00000e-9 to 9.99999e+9
Replace DAC Span Value DS={m.dd}E{+e}<CR> OK 1.00000e-9 to 9.99999e+9
Se/Store DAC Zero Value DZW OK
Set/Store DAC Span Value DSW OK
Notes:
The User Data is 10-digit text area reserved for use by the customer for identification purposes.
A setpoint may also be entered as a decimal number, e.g. [S1=0.760<CR>] will be same as entering
[S1=7.60E-1<CR>].
When inputting setpoint data, it should be entered in the same units of pressure as the presently
selected units of measurement (i.e. Torr, mbar or Pascal). The data is only checked to be a valid number
with a one-digit exponent before being accepted. There are no limit checks on the data; the user is free
to choose any value appropriate to his use of the instrument.
If the command syntax is not met or if the number is out or range, the Digital AVC will respond with the
ASCII codes for <bell>?<CR>, and the command will be ignored.

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3.6.4 Reset / Initialize Commands
Command Description Format Notes:
Software Reset /<CR> Reset instrument
Does not reset or overwrite any parameters saved in non-volatile memory (EEPROM).
Autobaud <ctrl-z><CR> Match baud rate currently in use
Device can run at 9600 or 19200 Baud. Set terminal to 9600/N/8/1 or 19200/N/8/1 and type Ctrl-Z.
The <ctrl-z> is entered by holding down the “Ctrl” key while pressing the “z” key when using terminal
emulator program. This character has an ascii code of 26 (decimal) and 1A (hexadecimal).
Device will respond with Device ID (Digital AVC). If this response is not generated, repeat the Ctrl-Z
until it is. The Baud rate will be stored in EEPROM and is remembered on the next power-up.
3.7 Operation and Performance
The Digital AVC will function right “out of the box”. For maximum accuracy refer to the Calibration section
below and perform the calibration procedure.
The simplest and quickest way of checking the operation and performance of a gauge and/or gauge tube,
is to keep a new or known-good gauge tube on hand for use as a reference.
To check operation, install both the reference and suspect gauge tubes in a common vacuum system
(locate the gauge tubes as close as possible to each other), then evacuate the system until a stable base
pressure is obtained. Alternately connect the vacuum gauge to each gauge tube and record its pressure
readings. If the gauge tube-under-test produces a significantly higher pressure reading than the reference
gauge tube, this indicates a calibration shift and is usually the result of contamination (particulate, oil, or
other chemical deposits). You can try to restore calibration of the contaminated gauge tube by cleaning it
internally with an appropriate solvent such as high-purity isopropyl alcohol (flood the interior cavity of
gauge tube gently with solvent and allow it to stand and soak for about 15 to 30-minutes). Drain the
contaminated solvent and let gauge tube dry in ambient air until all of the cleaning solvent has
evaporated. To prevent mechanical damage to the thermopile elements, do not use forced air to dry the
gauge tube. Gauge tubes that remain out of calibration after cleaning should be replaced.
3.8 Gauge Tube Operating Principle
Operation of the Hastings gauge
tube is based on a low voltage AC
bridge that heats a noble metal
thermopile. A change in pressure
in the gauge tube changes the
molecular collision rate and
therefore the thermal conduction
of the gas or gas mixture
surrounding the thermopile. This
results in a temperature shift in the
AC heated thermocouples A and
B. The resultant temperature shift
causes a change in the DC output
from couples A and B inversely
with pressure changes. The DC
thermocouple C (when installed) is
in series with the circuit load.
Thermocouple C provides
compensation for transient
changes in ambient temperature.