Tektronix Keithley AMM1F Master Analog Measurement Module Rev. A User manual

AMMI F
Master Analog Measurement Module

TheAMMlFAnaIogMeasurementModuIecombinesthree
important Series 500 functions into a single module. First,
the AMMlF functions as a standard analog input module,
and wiII accept up to 16 single-ended or eight differential
analog input signals. It contains signal conditioning and
switching circuitry for these channels. Second, the AMMlF
selects and conditions analog signals from other analog
input models in a Series 500. Last the AMMlF serves as a
12-bit A/D converter for its own analog input channels, as
well as any other analog signals which have been pro­cessed by the global select/conditioning circuitry. After
analog conditioning, signals are routed to the A/D con­verter section of the module for the analog-to-digital con­version process.

Input signals are applied to the AMMlF’s analog input
channels through on-card quick-connect screw terminals.
The AMMlF has a total of 16 local single-ended, or eight
differential inputs. The input configuration is controlled
through software, rather than with hardware switches.
These analog input channels can be conditioned with
programmable local gains of either xl or x10.

CAUTION
Always turn off the system power before in­stalling or removing modules. To minimize
the possibility of EMI radiation, always operate
the system with the top cover in place and
properly secured.

The AMMlF is designed to be used only in slot 1 of the 500­series system baseboard. To install the module, first re­move the baseboard top cover and install the module in
slot 1 with the component side facing the power supply.

High-speed Acquisition Mode with AMMl F

and ANINQ (SOFT500 and QUICK500)

The ANINQ command can operate the AMMlF module in
high-speed “auto-acquire” mode at an aggregated
throughput rate of up to 1OOkHz. Auto-acquire applies to
single or multiple channels. For multiple channels, the per­channel scan rate equals 1OOkHz divided by the number of
channels.

Global conditioning consists of a high-speed software­controIIed gain amplifier with programmable xl, x2, x5
and x10 gain values. AlI analog inputs connected to the
Series

500

pass through the global circuitry, whether the
signals originate on the AMMlF or some other analog
input module. Therefore, these gain values can be applied
to any analog input in the system.

For A/D conversion, the AMMlF uses a 12-bit successive
approximation converter. A maximum conversion time of
only 1Oi.t~~ allows sampling rates as high as 1OOkHz. To
maximize resolution, the AMMlF has 0-1OV and +lOV
A/D converter ranges which are software selectable.

Document Number: 501-924-01 Rev. A

The analog input module AIM2 can also provide up to

1OOkH.z throughput when used in a system containing an
AMMlE Other modules wiII give inaccurate results due to
slower settling times.

To operate the AMMlF in auto-acquire mode, you must
satisfy the following requirements:

1. The analog input channels sampled by ANINQ may be
on an AMMlF or AIM2.

2. Ah the channels sampled by the specific ANINQ com­mand must be on one module.

3. The AMMlF’s input filter must be set to 2OOkHz.

AMMlF/l

AMMlF
Master Analog Measurement Mode

If any of these conditions cannot be met, the speed of the
ANINQ command will revert to the speed of an ANIN
command. Under these circumstances, it is better to use
ANIN in order to take advantage of foreground/back­ground operating mode.

NOTE
TheANlNQcommandinSoft5OOandQuick500
has been optimized for auto-acquire (1OOkHz)
operation with the AMMlF. If you attempt
auto-acquiremodewithBASIC’sPEEK/POKE,
or the memory READ/WRlTE commands of
other languages, you may receive incorrect data.
If you do not use Soft500 or Quick500, Keithley
suggests that you run the AMMlF only in
“regular acquisition mode”. This mode is de­scribed under the heading “SELECT ACQLBSI­TION MODE” later in this manual.

Self-calibrating During “CALL INIT”(SOFT500
and QUCK500)

The AMMlF module performs a self-calibration each time
a CALL INlT is issued. Soft500 executes a CALL INIT each
time it is run in the non-resident mode, or just once when
it is loaded into memory in resident mode. Quick500
executes a CALL INIT each time it is loaded under the
QuickBASIC environment or with the “QRUN” option, or
just once when it is made resident with the “QLOAD”
option. Therefore, you need not issue a separate CALL
INlT specifically to calibrate the AMMlF.

single-ended local input configurations. These local input
signals are applied to screw terminals located toward the
rear portion of the AMMlF. Single-ended and differential
inputs use the same screw terminals.

The channel numbers are shown in Figure 2, which also
shows typical connections for channels 0 through 7 in
differential mode. For differential mode, connect the high
(+> side of an input signal to the (+> terminal, and the low
f-1 side of the signal to the corresponding (-> terminal.
When the AMMlF is configured for single-ended input,
connect the high (+> side of the input signal to one of the
terminals 0 through 15, and the low (-) side to either of the
two input low (-> terminals shown for single-ended inputs.
In Figure 2, the numbers listed in parentheses above the
lower connector are the single-ended local channels 9
through 15.

CAUTION
The AMMlF inputs
ended mode, one side of the input is con­nected to power line ground. Any signal con­nected to the AMMlF must also be referenced
to power line ground, or module or system
damage may occur. Also not that inaccuracies
on other channels may result. When used in
differential mode, the AMMlF local inputs
must both be within HOV of module ground
for proper operation. If either signal exceeds
k3OV module damage may result.

are non-isolated.

Insingle-

Soft500 and Quick500 will expect an AMMlF in the system
if the configuration file (CONFiG.TBL) shows an AMMlF
in slot 1. If the software cannot complete the calibration, it
will issue an error message such as “Unable to calibrate
A/D module”. If this occurs, check that:

1. The Series 500 is turned on.

2. The cable between Series 500 and IBIN interface is con­nected.

3. An AMMlF is mounted in slot 1 of the Series 500.

Connections and Operation

Signal Connection

The AMMlF can be programmed for either differential or

AMMlF/2

In many situations, shielded cable may be required to
minimize EMI radiation, or to keep noise to a minimum. If
shielded cable is used, connect the shield to ground only,
and do not use the shield as a signal-carrying lead. Usually,
a module ground terminal should be used, but in some
cases better results may be obtained by using one of the
baseboard ground posts. Use the configuration that results
in the lowest noise.

For shielding to be effective, the shield must contain both
high and low signal wires, and must not carry any other
signals. If a number of AMMlF signal input lines are
shielded, all shields should be connected to the same
ground terminal.

AMMlF

Master Analog Measurement Mode

Figure 2. Ah&W F Component Bayou t

Signal ground

-u-•

‘ilrrrrrlrmooooooooo

ICH7 CHOl

I

Shield ground

.

ID

:
: .

:
:
:
:

.

i

Single-ended

-IN (Input Low)

Figure 2. TypicaZ Difjerential Connection (Channel 0 Shown)

Module

GND

- 2 Measured
+ Voltage

Shield

(Optional)

I

AMMlF/3

AMMlF

Master Analog Measurement Mode

Signal Conditioning
Figure 3 shows a simplified block diagram of the AMMlF.

The module is divided into six general sections: a local
multiplexer, a local programmable gain amplifier, a global
multiplexer, a global programmable gain amplifier, a
programmable low-pass filter, and a 12-bit A/D converter.

Local input signals from channels 0 to 15 are applied to the
local multiplexer for selection. At any given time, only one
channel will be selected, as determined by the SELECT
CHANNEL command (covered later in this section). The
signal from the selected channel is then routed through a
local programmable gain amplifier to the global multi­plexer for further signal selection and conditioning.

The global multiplexer selects a single signal from among

the 10 slots in the system. In this manner, signals from any
of the 10 slots can be selected by software. The global
multiplexer is controlled by the SELECT SLOT command,
discussed later in this section.

After the signal is selected, the Global PGA applies soft­ware-selectable gains of xl, x2, x5, or x10. The signal finally

passes through a one-pole filter with software selectable -

3dB frequencies of either 2OOkHz or 2kHz. When this
signal conditioning process is complete, thesignalis routed
to the 12-bit A/D converter for digitization. After the
conversion process, digital data representing the applied
signal travels via the baseboard and interface card to the
host computer.

Input Filtering
Noise introduced into the input signal can corrupt the

accuracy of the measurement. Such noise will usually be
seen as an unsteady reading, or, in some cases, as a constant
offset. In the former case, the effects of noise will usually be
quite obvious, but may not be noticeable in the steady-state
offset situation.

Frequently, noise is introduced into the signal from 50 to
60Hz power sources. In many cases, noise can be attenu­ated by shielding or relocating the input signal lines, as
discussed earlier. It may also be possible to reject unwanted
60Hz noise by using the AMMlF in differential mode.
Since the 60H.z noise may also be present on the low side of
the signal, the differential amplifier will reject the common
signal. In more difficult situations, however, it may be
necessary to filter the input signal to achieve the necessary
noise reduction.

Programmable

Channel

Selection

Figure 3. AMMlF Signal Conditioning

AMMlF/4

-

’ - Programmable

Filter

2ookHz OR

PkHZ)

AMMIF

Master Analog Measurement Mode

When noise is a problem, a single-pole low-pass filter like

the one shown in Figure 4 can be connected between the

input signal and the corresponding AMMlF channel. Note

that the filter is made up of a single capacitor and resistor

with the capacitor connected between the AMMlF channel

input terminal and the module ground terminal. The resis­tor is then placed in series with the high input signal lead.

A common reference point for a simple filter like the one in
Figure 4 is the -3dB or half-power point, which is given as
follows:

f-=

1/(2zRC)

where f is in Hz, C is in farads, R is in ohms. Above this
frequency, filter response will roll off (decrease) at a rate of

-20dB per decade. Thus, each time the frequency increases
by a factor of 10, filter output voltage decreases by a factor
of 10 (-20dB).

To determine the relative RC values, the above equations
can be rearranged to solve for either R or C. If we wish to
choose a nominal capacitor value and then solve for the
resistance, we have:

R = 1/(2nCF~,)

Choosing a nominal value of 2l.tF for C, the necessary
resistance is:

R=1/(2nx(2x1O-?x6I-Iz)
R = 13.263k

The resulting response times with these R and C values
would be:

t(l%) = 4.6RC = 122ms
t(O.l%) = 6.9RC = 183ms
t(O.Ol%> = 9.2RC = 244ms

Note that there are a number of RC values that can be used

in a given situation. To

minimize the effects of the series

resistance, however, it is recommended that the value of R

be kept under 2OkQ.

Figure 4. Input Filtering

Although such filtering can quiet down a noisy signal,

there is a trade-off in the form of slower response. This
response time may be important in the case of a rapidly
changing input signal. For the filter in Figure 4, the re­sponse time to 1% of final value is 4.6RC, while the re­sponse times to 0.1% and 0.01% of final value are 6.9RC and

9.2RC, respectively.

As an example, assume that 10 counts of 6OHz noise is
present in the input signal. To reduce the noise to one
count, an attenuation factor of 10 (-20dB) at 6OHz will be
necessary. Thus, the filter should have a -3dB point of 6Hz.

Current-to-Voltage Conversion

AMMlF local inputs are designed to accept voltages in the
range of HOV. Thus, the AMMlFcan be directly connected
to many signal sources. Some transducers and instru­mentation, however, provide current outputs that must be

converted into voltages in order to be measured through
an AMMlF input channel.

When connecting current inputs to the AMMlF, a resistor
should be installed across the input to make the necessary
current-to-voltage conversion. J4, J5, and J6 provide loca­tions for installing these resistors on the Ah4MlF. Refer to

the circuit schematic and board layout diagrams for header
information.

The value of the resistor can be determined from Ohms
law as follows:

R=E/I

AMMlF/5

AMMZF

Master Analog Measurement Mode

Where R is the resistance in ohms, E is the maximum
desired voltage in volts (usually the upper range limit of
the A/D converter), and I is the maximum anticipated
current in amps.

As a example, assume the A/D converter is zero to +lOV
and that the expected current lies in the range of four to
40mA. The required resistance is:

R = lo/O.04
R=250

Thus, a 25OQ resistor should be installed across the input of
the channel in question (note that a 25Ofi value is required
when using Soft500 engineering units conversion). Since
current measurement accuracy is directly related to the
accuracy of the resistor, use the smallest tolerance resistor
available (typically 0.1%). Suitable 250&? precision resistors
can be purchased from Dale Resistors (P/N RN55E25OOB),
or from Keithley (P/N 500~RES-250).

Analog-to-Digital Converter Timing

When the AMMlF is in 1OOkHz auto acquire mode, the

trigger source can be set to either external or internal by the
J3 jumper. Place the jumper on pins 2 and 3 for internal
triggering. When set for internal triggering, the AMM2
continuously converts analog signals as described below
in the SET. ACQUISITION MODE command discussion.
When the J3 jumper is removed, a TTL-level signal can be
attached to pin 2 of the jrm-tper header with pin 3 used as a
ground. A low level applied to pin 2 will enable the
continuous conversion process, a high level applied to pin
2 will suspend the continuous conversion process. Place
the jumper on pins 1 and 2 to allow use of the TRGl
module. Models 575 and 576 have built-in TRGl modules,
or a TRGl may be placed in slot 2 of a 500A. In any case, the
application program must synchronize itself to the conver­sion process by polling the conversion status as explained
in the SELECT ACQUISITION MODE command discus­sion.

The pin configuration of the jumper header is as follows:
pin1 Path through backplane to TRGl module

pin2
pin 3 OV (ground)

trigger input with pull-up resistor to +5V

When programming high-speed sampling sequences,
certain timing constraints concerning the A/D conversion
cycle should be observed. Depending on the AMMlFs
acquire mode, the scenario for receiving converted values
from the A/D is very different. Refer to the discussion of
the acquire modes below for specific instruction on how to
process analog signals.

To increase system throughput, data latches have been
provided on the AMMlF, making data from the last con­version available while the converter is busy processing
another reading. The data is refreshed (updated) every
time a conversion has been completed.

External Trigger Operation

The AMMlF has the capability of triggering an acquisition

from an external ‘ITL-level source or from a TRGl module.

The jumper on the AMMlF fJ3) dictates the triggering

source. The external trigger can only be used in lOOkl!Iz
auto acquire mode which is explained below in the SET

ACQUISHION MODE command discussion.

The J3 jumper should be across pins 2 and 3 for internal
trigger operation. The jumper should be removed and the
external trigger source should be connected to pin 2 for
external rigger operation. The jumper should be across
pins 1 and 2 for operation with a TRGl module.

Commands

Table 1 summarizes the commands used with the AMMlF.
Note that several commands share the CMDA and CMDB
locations. Some commands use only selected bits in the

command byte, others are differentiated by whether a read
or write operation is performed.

The “xxx” in the address column signifies the three hexa-

decimal digits that make up the base hardware address
which is either switch selected or programmed on the
interface card. The suggested address is &HCFF80, so

h/,&./ = “&HCFF”.

AMMlF/6

Table 1. Commands Used with the AMMlF

AMMIF

Masfer Analog Measurement Mode

Command

SELECT CHANNEL
SELECT LOCAL CHANNEL MODE
SELECT LOCAL GAIN
SELECT ACQUJSITION MODE
SELECT FILTER
SELECT SLOT
SELECT CMDA READ MODE
SELECT RANGE
SELECT GLOBAL GAIN
RESET AND RECAL
A/D LOW DATA*
A/D STATUS*
A/D HIGH DATA
A/D START
EOC (end-of-conversion) STATUS

The information read from CMDA is selected by the SELECT CMDA READ MODE command. Refer to the
sections below for the foil description of their operations.

SELECT CHANNEL

Address Signal Line Bits Used

xxx80

xxx80
xxx80
XXX80
xxx80

xxx81

xx481
xxx81

xxx81
xxx9A
xxx80

xxx80

xxx81
xxx9B
xxx9B

CMDA (Write>
CMDA (Write)
CMDA (Write)
CMDA (Write)
CMDA (Write)
CMDB (Write)
CMDB (Write)
CMDB (Write)
CMDB (Write)
CMDC (Write)
CMDA (Read)
CMDA (Read)
CMDB (Read)
CMDD (Write)
CMDD (Read)

DO-D3
D4
D5
D6
D7
DO-D3
D4

D5
D6-D7
ALL
ALL
ALL
ALL
ALL
ALL

SELECT CHANNEL must be used in conjunction with the
SELECT SLOT command to select the channels on slot one

Location: xxx80

of the chassis.

The SELECT CHANNEL command is used to control the
local signal multiplexer on the AMMlF, thus determining
which of the local input channels is selected for A/D
conversion. This command affects only those signals con­netted to the AMMlF local inputs, and does not affect
input channels connected to modules located in other slots.

D7 D6 D5 D4 D3 D2 Dl DO Byte

L Channel Select: SE (O-15), DIFF (O-7)

Channel Mode: Single-ended (l), DIFF (0)
ACQ Mode: BOkHz Auto Acquire (i), Regular Acquire (0)

Filter Mode: 1OOkHz (0), 2kHz (1)

Note that the channel number occupies the least significant
four bits of CMDA. Make sure that the channel number is
combined with the appropriate upper four bits, as shown
in Figure 5, before it is sent.

Format

Figure 5. CMDA Wife Format (Address xxx80)

AMMlF/7

AMMlF

Master Analog Measurement Mode

Select Range: -lOV flOV (l), 0 flOV (0)
Select Global Gain: Xl (0), X2 (l), X5 (2), X10 (3)

Figure 6. CMDB Write Format (Address 23~81)

SELECT LOCAL CHANNEL MODE

Location: xxx80

The SELECT LOCAL CHANNEL MODE command con-

trols the configuration of the local input channels on the

AMMlF. The AMMlF input channels can be configured as

either 16 single-ended or eight differential input channels.
This command is selected by assigning a value to the D4 bit
position of CMDA as shown in Figure 5. A value of 1 will

set the inputs to single-ended, a value of 0 will set them to

differential.

Make sure that the other bits in the CMDA byte represents

the desired selection before it is sent.

SELECT LOCAL GAIN

Status (0), Low Data (1)

SELECT ACQUISITION MODE

The AMMlF has the capability of operating in either of two
modes; the regular acquisition mode, and the 1OOkHz auto
acquisition mode. As shown in Figure 5, the acquisition
mode is set by assigning a value to bit position D6 in
CMDA. Assigning a value of 0 enables regular acquisition
mode, a value of 1 enables 1OOkHz auto acquisition mode.

To acquire an analog reading when in the regular acqui­sition, the slot, channel, and gain must be selected. Then
after the appropriate settling time, the AMMlF is issued a
START CONVERSION command. At the time, the AMMlF
latches the signal and starts the digitization process. The
EOC STATUS command can be polled for end-of-con­version WC) after which the digitized value can be read.
The conversion process will consume approximately 1 Oj.lsec.

Location: xxx80
The gain applied to the local channels of the AMMlF is

programmable and can be set by assigning a value to bit

position D5 in CMDA. As shown in Figure 5, a value of 0

will apply a local gain of Xl and a value of 1 will apply a

local gain of X10 to the AMMlF input channels.

The local gain can be changed at any time as long as the

channel settling time is satisfied before the conversion is

started.

Make sure that the other bits in the CMDA byte represent

the desired selections before it is sent.

AMMlF/B

Since the incoming signal is latched when the START
CONVERSION command is issued, the slot, channel, and
gain selections can be changed immediately after the com­mand is issued. This will allow the settling time for the new
selections to be satisfied concurrently with the conversion
of the previous selection. This type of operation is not
required but will increase the throughput capability of
regular acquisition mode.

The 1OOkHz auto acquisition mode allows full 1OOkHz
acquisition speed on analog signals. Upon placing the
AMMlF in this mode, the A/D enters a free-running

1OOkHz conversion process. Do not attempt to issue the

START CONVElWON command in this mode.