Tektronix AMM2 User manual

AMM2

Master Analog Measurement Module

The AMM2 Analog Measurement Module combines three important Series 500 func­tions into a single module. First, the AMM2 functions as a standard analog input
module, and wiu accept up to 16 single-ended or eight differential analog input signals.
It contains signal conditioning and switching circuitry for these channels. Second, the
AMM2 selects and conditions analog signals from other analog input modules in a
Series 500. Last, the AMM2 serves as a 16-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 AMM2’s analog input channels through on-card quick­connect screw terminals. The AMM2 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.

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

500 pass through the global circuitry, whether the signals originate on the AMM2 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 AMM2 uses a l&bit successive approximation converter. A
maximum conversion time of only 20psec allows sampling rates as high as 5OkHz. To
maximize resolution, the AMM2 has O-XIV and &lOV A/D converter ranges which are
software selectable.

CAUTION: Always tum off the system power before installing or removing modules.
To minimize the possibility of EM1 radiation, always operate the system with the top
cover in place and properly secured.

The Ah4M2 is designed to be used only in slot 1 of the 500-series 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.

Document Number: 501-912-01 Rev. C

AMM2-1

AMM2-2

Figure 1. AMM2 Component Layout

High-speed Acquisition Mode with AMMP and ANINQ
(SOFT500 and QUICK500)

The ANINQ command can operate the AMM2 module in a high-speed “auto-acquire”
mode at an aggregate throughput rate of up to 5OkHz. Auto-acquire applies to single or
multiple channels. For multiple channels, the per-channel scan rate equals 5OkHz divid­ed by the number of channels.

The analog input modules AIM2 and AIM3 can also provide up to 5OkHz throughput
when these modules are used in a system containing an AMM2.

To operate the AMM2 in auto-acquire mode, you must satisfy the following
requirements:

1. The analog input channels sampled by ANINQ may be on an AMM2, AIM2, or
AIM3.

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

3. If the input channels are on an AlM3, the AIM3 must be set to xl gain.

4. The AMM2’s input filter must be set to lOOkI&.

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: The ANINQ command in Soft500 and Quick500 has been optimized for auto­acquire (5OkHz) operation with the AMM2. If you attempt auto-acquire mode with
BASIC’s PEEK/POKE, or the memory READ&VRlTE commands of other languages, you
may receive incorrect data. If you do not use Soft500 or Quick500, Keithley suggests
that you run the AMM2 only in “regular acquisition mode”. This mode is described
under the heading “SELECT ACQUISITION MODE” later in this manual.

Self-calibration During “CALL INIT” (SOFT500 and QUICK500)

The AMM2 module performs a self-calibration each time a CALL INIT 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 INIT specifically to calibrate the Ah&I2.

Soft500 and Quick500 will expect an AMM2 in the system if the configuration file

(CONFIGTBL) shows an AMM2 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 AMM2 is mounted in slot 1 of the Series 500.

AMM2-3

Connection and Operation

Signal Connection
The AMM2 can be programmed for either differential or single-ended local input con-

figurations. These local input signals are applied to screw terminals located toward the
rear portion of the AMM2. Single-ended and differential inputs use the same screw
terminals.

The channel numbers are shown in Figure 1. Figure 2 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 (-) side of the signal to the
corresponding (-) terminal. When the AMM2 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 the module ground at either end of the terminal strip. In Figure
the numbers listed in parentheses above the lower connector are the single-ended local
channels 9 through 15.

.’ ’ ’ ’ ‘Jl” ’ ’ ’ ’

eeeeeeeee@

GND 7+ 6+ 5+ 4+ 3+ 2+ l+ Cj+GND

2,

Measured

Voltage

” Shield

(Optional)

Series 500

Chassis Ground

t

I

1

Figure 2. Typical Differential Connection (Channel 0 Shown)

CAUTION: The AMM2 inputs are non-isolated. In single-ended mode, one side of the
input is connected to power line ground. Any signal connected to the AMM2 must
also be referenced to power line ground, or module or system damage may occur Also
note that inaccuracies on other channels may result. When used in differential mode,
the AMM2 local inputs must both be within flOV of module ground for proper
operation. If either signal exceeds k3OV module damage may result.

I

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 AMM2 signal input lines are
shielded, all shields should be connected to the same ground terminal.

Signal Conditioning

Figure 3 shows a simplified block diagram of the AMM2. 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 16-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 CHANN-S L 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 globalmultiplexer se!ects a sing!e signal from among the 10 s!ots 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 lOOkHz or 2kHz. When this signal conditioning process is
complete, the signal is routed to the 16-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.

Local
Programmable
Gain Amplifer

16 Single-ended or

8 Differential

inputs

(input Mode

Programmably

Selected)

Programmable

Locd

Channel

(Xl orX10)

-7

\L

Analog hyd.S

From Other

Slots e-

Global

Programmable

Gain Amplifier

(Xl .XZ,X6,OR

16Bl-r E

AlDAND =

SM-

f

Programmable

Filter

(1OOkHz OR

2kHz)

Figure 3. AMM2 Signal Conditioning

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 6OHz 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

AMM2-5

AMM2 in differential mode. Since the 6OHz 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. This is especially important to make good use of 16-bit A/D
resolution.

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 AMM2 channel.
Note that the filter is made up of a single capacitor and resistor with the capacitor con­nected between the AMM2 channel input terminal and the module ground terminal.
The resistor is then placed in series with the high input signal lead.

From Signal

To AMM2 Input

Figure 4. Input Filtering

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-m =

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).

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 fmal value are 6.9RC and

9.2RC, respectively.

1/(27rRC)

AMM2-6

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.

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/(2&f-,,,)

Choosing a nominal value of 2pF for C, the necessary resistance is:

R = 1427r x (2 x 10”) x 6Hz)

R = 13.263k

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

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

4.6RC = 122ms

Current-to-Voltage Conversion
AMM2 local inputs are designed to accept voltages in the range of &lOV. Thus, the

AMM2 can 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 AMM2 input channel.

When connecting current inputs to the AMM2, 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 AMh42. 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

Where R is the resistance in ohms, E is the maximum desired voltage in volts (usually

the upper range limit of the AID converter), and I is the maximum anticipated current

in amps.

As an example, assume the AID converter range is zero to +lOV and that the expected
current lies in the range of four to 401~~4. The required resistance is:

R

= 10/0.04

R = 250

Thus, a 25OQ resistor should be installed across the input of the channel in question
(note that a 2508 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 25OQ precision
resistors can be purchased from Dale Resistors, (PIN RN55E2500B), or from Keithley
(PIN 500-RES-250).

AMh42-7

Analog-to-Digital Converter Timing
When programming high-speed sampling sequences, certain timing constraints concern-

ing the AID conversion cycle should be observed. Depending on the AMM2’s 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 AMM2, 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 AMM2 has the capability of triggering an acquisition from an external TTLlevel
source. The jumper on the Ah4M2 (J3) dictates the triggering source. The external trig­ger can only be used in 5OkHz auto acquire mode which is explained below in the SET
ACQUISITION MODE command discussion.

When the AMM2 is in 5OkHz auto acquire mode, the trigger source can be set to either
external or internal by the J3 jumper. When set for internal triggering, the AMh42 con­tinuously converts analog signals as described below in the SET ACQUISITION MODE
command discussion. When the J3 jumper is removed, a TI’Llevel signal can be attach­ed to pin 2 of the jumper header. 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. In either 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:
pin 1 +5v

pin 2
pin 3

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 trigger operation

Commands

Table 1 summarizes the commands used with the AMM2. 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.

trigger input
OV (ground)

Table 1. Commands Used with the AMM2
Command

SELECT CHANNEL
SELECT LOCAL CHANNEL MODE
SELECT LOCAL GAIN
SELECT ACQUISITION MODE
SELECT FILTER

Address Signal Line
xxx80

xxx80
xxx80
x=80

xxx80
SELECT SLOT xxx81
SELECT CMDA READ MODE

xxx81
SELECT RANGE xxx81
SELECT GLOBAL GAIN

XXX81

RESET AND RECAL XXX9A
A/D LOW DATA! xxx80
A/D STATUS* xxx80
A/D HIGH DATA xxx81
A/D START xxx9B
EOC (end-of-conversion) STATUS

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)

Bits Used
DO-D3

D4
D5
D6
D7
DO-D3
D4
D5
D6-D7
ALL
ALL
ALL
ALL
ALL
ALL

* The information read from CMDA is selected by the SELECT CMDA READ MODE

command. Refer to the sections below for the full description of their operations.

The “xxx” in the address column signifies the three hexidecimal digits that make up the
base hardware address which is either switch selected or programmed on the interface
card. The suggested address is &HCFFBO, so “xxx” = “&HCFF”.

Select Channel, Local Gain, Filter, Acquisition Mode, and Channel Mode.

D5 D4 D3 D21 Dl DO

I

Channel Select: SE (O-15), DIFF (O-7)
Channel Mode: Single-ended (l), DIFF (0)
Local Gain: Xl (0), X10 (1)
ACQ Mode: 50kHz Auto Acquire (l), Regular Acquire (0)
Filter Mode: 1 OOkHz (0), 2kHz (1)

Figure 5. CMDA Write Format (Address xxx80)

AMM2-9

Select Slot, Range, Global Gain, and CMDA Read Mode.

D71D6 1 D5 1 D4jD3 D2( Di ID0

Byte Format

Select Slot: (O-15)

CMDA Read Mode: A/D Status

Select

Range: -1 OV +l OV

Select Global Gain: Xl (0), X2 (l), X5 (2), X10 (3)

(0),

Low Data

(l), 0 Cl OV (0)

(1)

Figure 6. CMDB Write Format (Address xxx81)

SELECT CHANNEL
Location: xxx80
The SELECT. CHANNEL command is used to control the local signal multiplexer on the

AMM2, thus determinin

g which of the local input channels
sion. This command affects only those signals connected to the AMM2 local inputs,
and does not affect input channels connected to modules located in other slots.
SELECT CHANNEL must be used in conjunction with the SELECT SLOT command to
select the channels on slot one of the chassis.

is selected

for A/D conver-

Note that the channel number occupies the least significant four bits of Ch4DA. Make
sure that the channel number is combined with the appropriate upper four bits, as
shown in Figure 5, before it is sent.

SELECT LOCAL CHANNEL MODE
Location: xxx80
The SELECT LOCAL CHANNEL MODE command controls the configuration of the

local input

channels on the

AMM2. The AMM2 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 represent the desired selections before
it is sent.

SELECT LOCAL GAIN
Location: xxx80

The gain applied to the local channels of the Ah&I2 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 AMM2 in­put channels.

AMM2-10