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SSI-4 Simple Sensor Interface 4 Channel
User Manual
SSI-4 Manual 1.2.doc
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1.
Overview............................................................................................................................... 3
1.1 Differential Inputs.............................................................................................................. 4
2. Specifications........................................................................................................................ 4
The Innovate Log-Chain concept....................................................................................................5
2.1 Log-Chain of 4 channels consisting of SSI-4 alone.......................................................... 6
2.2 6-channel Log-Chain example with 2 AFR channels........................................................ 6
2.3 16-Channel Log-Chain example....................................................................................... 6
3. Connecting the SSI-4............................................................................................................7
3.1 Connecting power............................................................................................................. 7
3.2 Connecting external sensor signals.................................................................................. 7
3.3 Powering external sensors................................................................................................ 7
4. RPM measurement............................................................................................................... 8
4.1 RPM Measurement basics................................................................................................ 8
4.1.1 Four-Stroke Engines.................................................................................................. 8
4.1.2 Two-Stroke Engines .................................................................................................. 8
4.1.3 Rotary Engines (Wankel Engine) .............................................................................. 9
4.2 How the SSI-4 determines RPM....................................................................................... 9
4.2.1 Measurement Method on Channel 1......................................................................... 9
4.3 Connecting an RPM signal (Channel 1) ........................................................................... 9
5. Measuring Frequencies, custom RPM, or speed............................................................... 10
6. Measuring duty cycle.......................................................................................................... 10
7. Measuring external 5V sensors.......................................................................................... 11
8. Programming the SSI-4 with LM Programmer ................................................................... 11
8.1 Changing the device name.............................................................................................12
8.2 Updating the firmware..................................................................................................... 12
8.3 Input Configurations....................................................................................................... 12
8.3.1 Measuring RPM (Input 1 only)................................................................................. 12
8.3.2 Measuring Frequency (all Inputs)............................................................................ 13
8.3.3 Measuring Speed (all Inputs)................................................................................... 13
8.3.4 Measuring Duty Cycle (Input 2 only) ....................................................................... 14
9. Kit Contents........................................................................................................................15
Appendix A: Limited Warranty...................................................................................................... 16
Revision History............................................................................................................................. 16
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1. Overview
The SSI-4 device is a simple sensor interface device to add 4 inputs to an MTS Log Chain. The
SSI-4 may also be used as a stand-alone 4 channel MTS compatible input device (see Chapter 2
for more details).
Each of the four inputs of the SSI-4 can be user configured for different functionalities.
The following tables show the functionality of each of the 4 inputs of the SSI-4 (the default factory
settings of the SSI-4 are highlighted:
Input Function 1 Function 2 Function 3
Channel 1
RPM
(programmable
Range, default
0..10230 RPM, 4
Frequency
(straight
frequency,
Speed sensor)
External 0..5
Volt
Cylinder)
Channel 2 Duty Cycle
Channel 3 N/A
Channel 4
Frequency
(straight
frequency,
Speed sensor)
Frequency
(straight
frequency,
Speed sensor)
Frequency
(straight
frequency,
Speed sensor)
External 0..5
Volt
External 0..5
Volt
External 0..5
Volt
The SSI-4 also can act as a power supply for user supplied external sensors. The 5V output of
the SSI-4 can supply up to 300mA of current.
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1.1 Differential Inputs
The SSI-4’s external connections are differential. This means that each input channel has 2 input
terminals. A + terminal and a – terminal. This is to eliminate ground offsets in the signal. Many
times the ground point of a sensor is at a different ground than the SSI-4. Because an electronic
device can only measure a voltage referenced to it’s own ground, differences in grounding can
introduce measurement errors. The SSI-4 measures the sensor signal’s ground with the – input
and them measures the difference between the + and the – input. This way it “recreates” the
sensor signal’s own ground reference as if this input were referenced directly to that sensor’s
ground. The common mode rejection range is the maximum voltage this ground reference input
can differ from the SSI-4 ground.
The (–) input is NOT a ground itself. It is a ground reference input.
2. Specifications
Power
Power requirements
Power reversal protection Yes
External Sensor power 5V (+- 2.5%), 300mA max.
Serial Communication
Serial Port Speed 19.2 kbit/sec
Packet/Logging Speed 81.92 msec/sample packet
Sample Resolution 10 bits (0..5V at 0.1% resolution)
Input Specifications
Number of Channels 4
Input measurement range 0..5V
CHx+ max input voltages - 22.5 Volt to +300 Volt
CHx- max input voltages - 22.5 Volt to +27.5 Volt
Common Mode Rejection
Range
Input threshhold for pulsed
Signals
Max Frequency
Input Impedance 1 MOhm
Temperature
Max Operating Temperature -20 to +80 deg Celsius
Mechanical
Size (W x L x H) 133 x 65 x 26 mm
Weight 114 grams
Note 1:
Supply current specified does not include external sensor current supplied by 5V output.
Note 2:
Sum of all frequency/Duty Cycle signals connected should not exceed 15 kHz.
8-36 Volt / 50mA
-22.5 Volt to +22.5 Volt
2.5V
2
15 kHz
1
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The Innovate Log-Chain concept
LogWorks 2.0 has the capability to log, display and analyze up to 32 engine parameters. Most
users will use less though. Each of the MTS components reads between 1 and 6 engine
parameters. To interface a multitude of MTS components to LogWorks with a single connection,
the Innovate LogChain concept was introduced.
The SSI-4 can be used as a MTS component in a Log-Chain.
Each of the MTS components has two serial ports (except the LM-1, which has only one). One
serial port is designated as IN-port, the other as OUT port. The OUT-port of one device is
connected to the IN-port of the next device and so on. This way devices can be ‘daisy-chained’ to
build a log-chain for up to 32 channels total. The OUT-port of the last device is connected to the
computer for logging or downloading of logged data.
The device that’s first in the chain is special. It determines the logging sample rate. The first
device in the chain sends a data packet containing its channel data (a sample) to the next device
(downstream, left to right in the diagram) every 81.92 milliseconds. The next device appends its
data to that packet and hands that packet to the next device downstream and so on. At each
device the packet grows in length. The devices in the chain synchronize their sampling of the
engine parameters to the packets, so that all the channels in a packet together represent the
same instance in time. At the downstream end of the log chain (OUT-port of the last device) a
computer or external logger can be connected to store or display the stream data. The XD-1
display is such a device.
This also means that the complete channel data set is ONLY available at the end of the
log-chain. A datalogger capable of recording the log-chain data-stream therefore MUST be
placed at the end of the log-chain. This includes lap-top computers or other loggers.
Commands for individual devices are sent ‘upstream’. A device (incl. a computer or an XD-1) can
send commands to the devices upstream of itself, but not downstream. Commands can include
start-stop recording, calibration/configuration commands and so on. Only the device directly
upstream of the command originator of course will receive the command. This device then
decides, depending on the command, whether to execute the command and whether to pass it
on. An example of a case where the command is executed but not passed on is the start-stop
record command. The first upstream device capable of logging internally will execute the
command, but not pass it on.
As said before, the first device is special because it is the synchronization source for the entire
chain. By plugging its IN-port with the supplied terminator connector, a device can detect that
requirement when it powers up. The terminator connector just connects the transmit and receive
line of the IN-port together. Each device sends a special command out on it’s IN port when it
powers up. This command is ignored and not passed on by any device if received on it’s OUT
port. If the sending device immediately receives that command on its IN-port again, because the
terminator is plugged in, it assumes it is the first and special device in the chain. The LM-1,
having only one serial port, is ALWAYS a special device and MUST be connected to the
beginning of the chain.
The following are some examples of Log-Chains using the SSI-4 and other MTS devices.
NOTE: The SSI-4 does NOT need a terminator plug on it’s IN port. It
automatically detects if another device is plugged into it’s IN port and
terminates the IN port if nothing is plugged in.
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