SRS Labs SIM928 Operation manual

Operation and Service Manual
Isolated Voltage Source
SIM928
Stanford Research Systems
Revision 2.0 •August 25, 2006

Certification
Stanford Research Systems certifies that this product met its published specifications at the time
of shipment.
Warranty
This Stanford Research Systems product is warranted against defects in materials and workman-
ship for a period of one (1) year from the date of shipment.
Service
For warranty service or repair, this product must be returned to a Stanford Research Systems
authorized service facility. Contact Stanford Research Systems or an authorized representative
before returning this product for repair.
Information in this document is subject to change without notice.
Copyright c Stanford Research Systems, Inc., 2005, 2006. All rights reserved.
Stanford Research Systems, Inc.
1290–D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: [phone] •Fax: [phone]
www.thinkSRS.com •e-mail: [email protected]
Printed in U.S.A. Document number 9-01593-903
SIM928 Isolated Voltage Source

Contents
General Information iii
Safety and Preparation for Use . . . . . . . . . . . . . . . . iii
Symbols ............................. iv
Notation ............................. v
Specifications .......................... vi
1 Getting Started 1 – 1
1.1 Introduction to the Instrument . . . . . . . . . . . . . 1 – 2
1.2 Front-Panel Operation . . . . . . . . . . . . . . . . . . 1 – 2
1.3 SIMInterface........................ 1–6
2 Remote Operation 2 – 1
2.1 Index of Common Commands . . . . . . . . . . . . . . 2 – 2
2.2 Alphabetic List of Commands . . . . . . . . . . . . . . 2 – 4
2.3 Introduction ........................ 2–6
2.4 Commands......................... 2–7
2.5 StatusModel........................ 2–17
3 Circuitry 3 – 1
3.1 Circuit Description . . . . . . . . . . . . . . . . . . . . 3 – 2
3.2 PartsList.......................... 3–7
3.3 Schematic Diagrams . . . . . . . . . . . . . . . . . . . 3 – 7
i

ii Contents
SIM928 Isolated Voltage Source

General Information
The SIM928 Isolated Voltage Source, part of Stanford Research Sys-
tems’ Small Instrumentation Modules family, is a low-noise pro-
grammable voltage source intended for sensor biasing and other
demanding, low-power applications. Dual, auto-switching inter-
nal nickel-metal-hydride batteries provide continuous uninterrupted
operation at the isolated output, which can deliver up to ±20 V bias
at up to ±10 mA current load.
Safety and Preparation for Use
The front-panel binding post outputs (+and −) are isolated from
the Earth, the power-line-outlet ground, and the metal chassis of
the module. No dangerous voltages are generated by the SIM928.
However, if a dangerous voltage is externally applied to the module,
WARNING it may be present on (either) binding post connector, the chassis, or
the SIM interface connector, and may cause injury or death.
Do not exceed ±40 V to the Earth at either binding post terminal.
The SIM928 ships from the factory with the internal battery pack
installed and ready for operation. Do not install substitute parts or
perform any unauthorized modifications to this instrument.
The SIM928 is a single-wide module designed to be used inside the
SIM900 Mainframe. Do not turn on the power until the module is
completely inserted into the mainframe and locked in place.
iii

iv General Information
Symbols you may Find on SRS Products
Symbol Description
Alternating current
Caution - risk of electric shock
Frame or chassis terminal
Caution - refer to accompanying documents
Earth (ground) terminal
Battery
Fuse
On (supply)
Off (supply)
SIM928 Isolated Voltage Source

General Information v
Notation
The following notation will be used throughout this manual.
A warning means that injury or death is possible if the instructions
WARNING are not obeyed.
A caution means that damage to the instrument or other equipment
CAUTION is possible.
Typesetting conventions used in this manual are:
•Front-panel buttons are set as [Button];
[Adjust ] is shorthand for “[Adjust ] & [Adjust ]”.
•Front-panel indicators are set as Overload.
•Remote command names are set as *IDN?.
•Literal text other than command names is set as OFF.
Remote command examples will all be set in monospaced font. In
these examples, data sent by the host computer to the SIM928 are set
as straight teletype font, while responses received by the host
computer from the SIM928 are set as slanted teletype font.
SIM928 Isolated Voltage Source

vi General Information
Specifications
Performance Characteristics
Min Typ Max Units
Output Output range −20 +20 V
Floating output −40 +40 V (common mode to ground)
Noise 10 µVrms, 1 kHz BW
Settable resolution 1 mV
Display resolution 1 mV, |V|<1.999 V
10 mV, |V|<19.99 V
Max. output current −10 +10 mA (before dropout)
Short circuit current ±15 mA
Short circuit duration indefinite
Batteries Number of batteries 2 1 operating, 1 charging/standby
Chemistry Nickel metal hydride
Charge time 5 h
Discharge time 12 h (10 mA load)
Lifetime 1000 charge cycles, 2 yr shelf life
Battery switching Automatic, when active battery is fully discharged
Switchover glitch <1 mV for <1 ms
Battery charge override Allows manual switching of batteries. Triggered when
[Battery Override] is held for 5 s or more. Only armed
when standby battery is in ready state
Operating Temperature 0 40 ◦C
Power −15,+5,+24 V DC
Supply current 250 mA (+5 V)
40 mA (−15,+24 V)
General Characteristics
Interface Serial (RS-232) through SIM interface
Connectors Banana binding posts (+,−, and chassis ground)
DB–15 (male) SIM interface
Weight 3 lbs
Dimensions 1.500 W×3.600 H×7.000 D
SIM928 Isolated Voltage Source

1 Getting Started
This chapter gives you the necessary information to get started
quickly with the SIM928 Isolated Voltage Source.
In This Chapter
1.1 Introduction to the Instrument . . . . . . . . . . . . 1 – 2
1.1.1 Overview .................... 1–2
1.1.2 Power-on State . . . . . . . . . . . . . . . . . 1 – 2
1.2 Front-Panel Operation . . . . . . . . . . . . . . . . . 1 – 2
1.2.1 Adjust ...................... 1–3
1.2.2 Battery...................... 1–4
1.2.3 Output...................... 1–5
1.3 SIMInterface ...................... 1–6
1.3.1 SIM interface connector . . . . . . . . . . . . 1 – 6
1.3.2 Direct interfacing . . . . . . . . . . . . . . . . 1 – 7
1–1

1–2 Getting Started
1.1 Introduction to the Instrument
The SIM928 Isolated Voltage Source is ideally suited for applications
demanding flexibility and low-noise from a programmable voltage
source.
1.1.1 Overview
The basic function of the SIM928 is to generate a user-specified volt-
age, between −20 V and +20 V, between the +and −front-panel
terminals. The architecture of the SIM928 uses an internal battery
to power the output stage. This provides an ideal voltage source,
free of power-supply ripple. Two independent batteries are used;
while one is powering the output circuitry, the second is either be-
ing recharged or held in standby. When the output battery nears
its fully-discharged state, the standby battery is seamlessly switched
into the output circuit, and the depleted battery switched to the inter-
nal charger. With this arrangement, essentially continuous isolated
bias voltage is available to the user.
Note that, although the output stage is energized by internal storage
batteries, the control circuitry is powered externally (typically, by the
SIM900 Mainframe). Absent any external power, the SIM928 will be
off.
1.1.2 Power-on State
The SIM928 stores its operation state (programmed voltage and
on/offconfiguration) in non-volatile memory. At power-on, the
SIM928 will return to its previous configuration after a brief system
check and initialization.
The power-on system check includes a brief test of both internal bat-
teries. If either battery appears fully discharged, it will be switched
onto the internal charger circuit; if both batteries appear discharged
(as can occur after an extended storage period), the SIM928 will not be
able to turn on the output stage. In this case, you should allow aboutfirst use after extended storage
5–6 hours of powered operation to bring the first battery up to full
charge, at which time it will switch to the On state and begin charging
the second battery. This period can be shortened by power-cycling
the SIM900 Mainframe, which will cause the SIM928 to re-initiate it’s
power-on checks. Note that at least 1–2 hours should be allowed to
provide a sufficient partial charge for reasonable operation.
1.2 Front-Panel Operation
The front panel of the SIM928(see Figure 1.1) provides a simple op-
erator interface.
SIM928 Isolated Voltage Source

1.2 Front-Panel Operation 1–3
Figure 1.1: The SIM928 front and rear panels.
1.2.1 Adjust
Routine operation of the SIM928 is through the front panel “ADJUST”
block.
1.2.1.1 On/Off toggle
The output circuit of the SIM928 is toggled between enabled and
disabled with [On/Off]. In the event of an overvoltage Trip (see
section 1.2.3.2), press [On/Off] to clear the Trip indicator.
1.2.1.2 Changing the programmed voltage
The remaining 6 adjust keys allow changing the programmed voltage
from the front panel. Brief taps on [100 mV ] increment or decre-
ment the setting by 100 mV; similarly, the [10 mV ] and [1 mV ]
step the setting by 10 mV and 1 mV, respectively. Holding any of
these keys for 1 second begins an (accelerating) auto-repeat for faster
voltage changes. Note that the auto-repeat function will not scroll
across 0 V; when decreasing a positive setting, or increasing a nega-
tive setting, the auto-repeat will stop at 0 V. To reverse the polarity,
the key must be released and then re-pressed to resume auto-repeat.
Note that the programmed voltage can be modified independent of
the on/offstate of the SIM928. Adjusting the voltage while in the On
SIM928 Isolated Voltage Source

1–4 Getting Started
state causes the output voltage to change in real time.
When the programmed voltage |V|<1.999 V, the display shows the
full settable resolution of the SIM928. At greater voltages (|V|>
1.999 V) the least significant digit shown corresponds to 10 mV. It is
still possible to make discrete 1 mV steps using [1 mV ]; by counting
key taps, the user can determine the sub-display voltage setting.
When |V| ≥ 2.00 V, the display always corresponds to the truncated
value of the programmed voltage. For instance, if V= +2.120 V
through +2.129 V, the display will show ; similarly, if V=
−12.730 V through −12.739 V, the display will show .
1.2.2 Battery
The “BATTERY” block of the front panel shows the present state of
the SIM928’s internal battery system. The two batteries, labeled “A”
and “B”, correspond to the two shaded rows, while the available bat-
tery states On,Charge, and Ready correspond to the three columns.
A battery is On when it is switched to power the output stage; Ready
corresponds to a battery in the (nominally) fully-charged state that
is ready for operation when the On battery is depleted. The Charge
state indicates that the battery is connected to the charger circuit.
1.2.2.1 Battery cycle
Under typical operation, a fully charged battery should run for 12–
18 hours before being depleted. When the On battery is nearly dis-
charged, an internal threshold circuit signals the SIM928 controller to
begin a battery switch-over. The stand-by battery (which at this point
is typically in the Ready state) is switched onto the output circuit,
after which the discharged battery is switched to the charger cir-
cuit. A “diode-or” circuit effectively prevents the discharged battery
from loading down the fresh battery, and the output driver operates
without interuption.1.
When the discharged battery is first connected to the charger circuit,
a resistive load is briefly applied to complete the discharge of the cell
to a known starting voltage. From that point, the charger applies a
fixed charging current for ∼5 hours to completely charge the battery.
If power is interrupted while the battery is charging, the charge cy-
cle will not resume; rather, the power-on system check will select
the most depleted battery for initial operation and place the other
battery in the Ready state (assuming neither battery appears fully
discharged). This algorithm ensures that a battery cannot be over-
charged by an unfortunate series of power-cycles.
1A small glitch may appear at the output when the fresh battery switches in
SIM928 Isolated Voltage Source

1.2 Front-Panel Operation 1–5
1.2.2.2 Battery charge override
For some applications, it may be important to insure that the SIM928
will not begin a battery switch-over during a particularly sensitive
experiment. The [Battery Override] can be used to force the Ready
battery to be switched to On immediately, ensuring a 12+hour period
of un-switched operation.
The [Battery Override] is only armed when one of the batteries is
in the Ready state; while a battery is in the Charge state, this key
is temporarily disabled. To initiate a forced swich-over, press and
hold [Battery Override] for at least 5 seconds. Over the next few
seconds, the standby battery will be switched in, and the previously
On battery will be switched to the standby (Ready) state—not to the
charger—where it will remain.
1.2.2.3 Service batteries
The nickel-metal-hydride battery packs used in the SIM928 have a
finite lifetime. After around 1000 charge/discharge cycles, the re-
maining battery capacity is significantly reduced; to restore the in-
strument to full performance, the battery pack must be replaced. The
yellow service batteries indicator turns on when the battery pack has
reached this limit. The SIM928 will continue to operate properly with
reduced-capacity batteries; the only effect will be the battery switch-
over will occur more frequently.
It is also possible, if a SIM928 is left in storage for several years with-
out operation, that the batteries will have lost a significant fraction of
their capacity due to aging. In this case, the yellow service batteries
indicator will not turn on, but the user may notice a shorter period
between battery charge cycles. The manufacture date of the battery
pack can be determined with the remote BIDN? query.
Replacement battery packs can be ordered from Stanford Research
Systems.
1.2.3 Output
The SIM928 output voltage is available at the front-panel between
the red +and black −banana jack/binding posts. These connectors
accept standard 0.175” in Banana plugs. The binding post accomo-
dates wire leads up to #12 AWG, as well as open spade lugs for #8
studs (0.165” minimum opening).
The lower, green terminal is tied to the SIM928 chassis, and is avail-
able for user grounding. Either output terminal may be tied to chassis
ground, if desired.
SIM928 Isolated Voltage Source

1–6 Getting Started
1.2.3.1 Output Overload
The SIM928 is specified to maintain its programmed voltage dif-
ference between the output terminals for load currents smaller than
±10 mA. If an low-impedance load causes the output current to reach
around ±15 mA, the output will go into current-limit mode, and the
red OVLD indicator will turn on. The SIM928 can remain in over-
load indefinitely, and will return to its programmed output voltage
as soon as the load current is reduced.
1.2.3.2 Overvoltage / TRIP
In addition to its current-limiting circuitry, the SIM928 has an over-
voltage sensing circuit that detects excessive voltage across the out-
put terminals. If the voltage across the outputs exceeds ∼ ±30 V, this
protection circuitry disconnects the output driver from the output
terminals, and the red Trip indicator will turn on. Typically, an over-
voltage TRIP is generated by some external voltage applied to the
SIM928 across its output terminals.
To clear an overvoltage TRIP, press [On/Off]. This will return the
SIM928 to the Offstate; a second press of [On/Off] will attempt to
switch the instrument back on. If the overvoltage condition still
exists, the output will again trip off.
1.3 SIM Interface
The primary connection to the SIM928 Isolated Voltage Source is the
rear-panel DB–15 SIM interface connector. Typically, the SIM928 is
mated to a SIM900 Mainframe via this connection, either through
one of the internal Mainframe slots, or the remote cable interface.
It is also possible to operate the SIM928 directly, without using the
SIM900 Mainframe. This section provides details on the interface.
The SIM928 has no internal protection against reverse polarity, missing
CAUTION supply, or overvoltage on the power supply pins. Misapplication of power
may cause circuit damage. SRS recommends using the SIM928 together
with the SIM900 Mainframe for most applications.
1.3.1 SIM interface connector
The DB–15 SIM interface connector carries all the power and commu-
nications lines to the instrument. The connector signals are specified
in Table 1.1
SIM928 Isolated Voltage Source

1.3 SIM Interface 1–7
Direction
Pin Signal Src ⇒Dest Description
1 SIGNAL GND MF ⇒SIM Ground reference for signal
2−STATUS SIM ⇒MF Status/service request (GND =asserted, +5 V=idle)
3 RTS MF ⇒SIM HW handshake (+5 V=talk; GND =stop)
4 CTS SIM ⇒MF HW handshake (+5 V=talk; GND =stop)
5−REF 10MHZ MF ⇒SIM 10 MHz reference (optional connection)
6−5 V MF ⇒SIM Power supply (no connection in SIM928)
7−15 V MF ⇒SIM Power supply (battery charger)
8 PS RTN MF ⇒SIM Power supply return
9 CHASSIS GND Chassis ground
10 TXD MF ⇒SIM Async data (start bit =“0”= +5 V; “1” =GND)
11 RXD SIM ⇒MF Async data (start bit =“0”= +5 V; “1” =GND)
12 +REF 10MHz MF ⇒SIM 10 MHz reference (optional connection)
13 +5 V MF ⇒SIM Power supply (digital circuitry)
14 +15 V MF ⇒SIM Power supply (no connection in SIM928)
15 +24 V MF ⇒SIM Power supply (battery charger)
Table 1.1: SIM Interface Connector Pin Assignments, DB-15
1.3.2 Direct interfacing
The SIM928 is intended for operation in the SIM900 Mainframe, but
users may wish to directly interface the module to their own systems
without the use of additional hardware.
The mating connector needed is a standard DB–15 receptacle, such as
Amp part # 747909-2 (or equivalent). Clean, well-regulated supply
voltages of −15,+5,+24 VDC must be provided, following the pin-out
specified in Table 1.1. Ground must be provided on pins 1 and 8,
with chassis ground on pin 9. The −STATUS signal may be monitored
on pin 2 for a low-going TTL-compatible output indicating a status
message.
1.3.2.1 Direct interface cabling
If the user intends to directly wire the SIM928 independent of the
SIM900 Mainframe, communication is usually possible by directly
connecting the appropriate interface lines from the SIM928 DB–15
plug to the RS-232 serial port of a personal computer.2Connect RXD
from the SIM928 directly to RD on the PC, TXD directly to TD, and
similarly RTS→RTS and CTS→CTS. In other words, a null-modem
style cable is not needed.
2Although the serial interface lines on the DB-15 do not satisfy the minimum
voltage levels of the RS-232 standard, they are typically compatible with desktop
personal computers
SIM928 Isolated Voltage Source

1–8 Getting Started
To interface directly to the DB–9 male (DTE) RS-232 port typically
found on contemporary personal computers, a cable must be made
with a female DB–15 socket to mate with the SIM928, and a female
DB–9 socket to mate with the PC’s serial port. Separate leads from
the DB–15 need to go to the power supply, making what is sometimes
know as a “hydra” cable. The pin-connections are given in Table 1.2.
DB–15/F to SIM928 Name
DB–9/F
3→ 7 RTS
4→ 8 CTS
10 → 3 TxD
11 → 2 RxD
5 Computer Ground
to P/S
7→ −15 VDC
13 → +5 VDC
15 → +24 VDC
8,9 → Ground (P/S return current)
1→ Signal Ground (separate wire to Ground)
Table 1.2: SIM928 Direct Interface Cable Pin Assignments
1.3.2.2 Serial settings
The initial serial port settings at power-on are: 9600 Baud, 8–bits, no
parity, 1 stop bit, and RTS/CTS flow control. These may be changed
with the BAUD,FLOW, or PARI commands.
The maximum standard baud rate that the SIM928 supports is 38400.
The minimum baud rate is 110. Above 38400, the SIM928 can be
set to the following (non-RS-232-standard) baud rates: 62500, 78125,
104167, 156250. Note that these rates are typically not accessible on
a standard PC RS-232 port, but can be used between the SIM928 and
the SIM900 Mainframe.
SIM928 Isolated Voltage Source

2 Remote Operation
This chapter describes operating the SIM928 over the serial interface.
In This Chapter
2.1 Index of Common Commands . . . . . . . . . . . . 2 – 2
2.2 Alphabetic List of Commands . . . . . . . . . . . . 2 – 4
2.3 Introduction....................... 2–6
2.3.1 Power-on configuration . . . . . . . . . . . . 2 – 6
2.3.2 Buffers ...................... 2–6
2.3.3 Device Clear . . . . . . . . . . . . . . . . . . . 2 – 6
2.4 Commands ....................... 2–7
2.4.1 Command syntax . . . . . . . . . . . . . . . . 2 – 7
2.4.2 Notation..................... 2–8
2.4.3 Examples .................... 2–8
2.4.4 Output commands . . . . . . . . . . . . . . . 2 – 9
2.4.5 Battery commands . . . . . . . . . . . . . . . 2 – 9
2.4.6 Serial communication commands . . . . . . 2 – 10
2.4.7 Status commands . . . . . . . . . . . . . . . . 2 – 11
2.4.8 Interface commands . . . . . . . . . . . . . . 2 – 13
2.5 StatusModel ...................... 2–17
2.5.1 Status Byte (SB) . . . . . . . . . . . . . . . . . 2 – 18
2.5.2 Service Request Enable (SRE) . . . . . . . . . 2 – 19
2.5.3 Standard Event Status (ESR) . . . . . . . . . 2 – 19
2.5.4 Standard Event Status Enable (ESE) . . . . . 2 – 20
2.5.5 Communication Error Status (CESR) . . . . . 2 – 20
2.5.6 Communication Error Status Enable (CESE) 2 – 21
2.5.7 Overload Status (OVCR) . . . . . . . . . . . . 2 – 21
2.5.8 Overload Status (OVSR) . . . . . . . . . . . . 2 – 21
2.5.9 Overload Status Enable (OVSE) . . . . . . . . 2 – 22
2–1

2–2 Remote Operation
2.1 Index of Common Commands
symbol definition
i,jIntegers
fFloating-point values
zLiteral token
(?) Required for queries; illegal for set commands
var Parameter always required
{var}Required parameter for set commands; illegal for queries
[var] Optional parameter for both set and query forms
Output
VOLT(?) {f}2 – 9 Voltage
OPON 2 – 9 Output On
OPOF 2 – 9 Output Off
EXON(?) {z}2 – 9 Excitation On/Off
Battery
BCOR 2 – 9 Battery charger override
BATS? 2 – 10 Battery State
BIDN? z 2 – 10 Battery Identification
Serial Communications
BAUD(?) {i}2 – 11 Baud Rate
FLOW(?) {z}2 – 11 Flow Control
PARI(?) {z}2 – 11 Parity
Status
*CLS 2 – 11 Clear Status
*STB? [i]2 – 12 Status Byte
*SRE(?) [i,]{j}2 – 12 Service Request Enable
*ESR? [i]2 – 12 Standard Event Status
*ESE(?) [i,]{j}2 – 12 Standard Event Status Enable
CESR? [i]2 – 12 Communication Error Status
CESE(?) [i,]{j}2 – 12 Communication Error Status Enable
OVCR? [i]2 – 13 Overload Condition
OVSR? [i]2 – 13 Overload Status
OVSE(?) [i,]{j}2 – 13 Overload Status Enable
PSTA(?) {z}2 – 13 Pulse −STATUS Mode
Interface
*RST 2 – 13 Reset
CONS(?) {z}2 – 14 Console Mode
*IDN? 2 – 14 Identify
SIM928 Isolated Voltage Source

2.1 Index of Common Commands 2–3
*OPC(?) 2 – 14 Operation Complete
LEXE? 2 – 14 Execution Error
LCME? 2 – 15 Device Error
LBTN? 2 – 15 Button
TOKN(?) {z}2 – 16 Token Mode
TERM(?) {z}2 – 16 Response Termination
SIM928 Isolated Voltage Source

2–4 Remote Operation
2.2 Alphabetic List of Commands
?
*CLS 2 – 11 Clear Status
*ESE(?) [i,]{j}2 – 12 Standard Event Status Enable
*ESR? [i]2 – 12 Standard Event Status
*IDN? 2 – 14 Identify
*OPC(?) 2 – 14 Operation Complete
*RST 2 – 13 Reset
*SRE(?) [i,]{j}2 – 12 Service Request Enable
*STB? [i]2 – 12 Status Byte
B
BATS? 2 – 10 Battery State
BAUD(?) {i}2 – 11 Baud Rate
BCOR 2 – 9 Battery charger override
BIDN? z 2 – 10 Battery Identification
C
CESE(?) [i,]{j}2 – 12 Communication Error Status Enable
CESR? [i]2 – 12 Communication Error Status
CONS(?) {z}2 – 14 Console Mode
E
EXON(?) {z}2 – 9 Excitation On/Off
F
FLOW(?) {z}2 – 11 Flow Control
L
LBTN? 2 – 15 Button
LCME? 2 – 15 Device Error
LEXE? 2 – 14 Execution Error
O
OPOF 2 – 9 Output Off
OPON 2 – 9 Output On
OVCR? [i]2 – 13 Overload Condition
OVSE(?) [i,]{j}2 – 13 Overload Status Enable
OVSR? [i]2 – 13 Overload Status
P
PARI(?) {z}2 – 11 Parity
SIM928 Isolated Voltage Source