CIO-SSH16 USER’S MANUAL Revision 3 October, 2000
MEGA-FIFO, the CIO prefix to data acquisition board model numbers, the PCM prefix to data acquisition board model numbers, PCM-DAS08, PCM-D24C3, PCM-DAC02, PCM-COM422, PCM-COM485, PCM-DMM, PCM-DAS16D/12, PCM-DAS16S/12, PCM-DAS16D/16, PCM-DAS16S/16, PCI-DAS6402/16, Universal Library, InstaCal, Harsh Environment Warranty and Measurement Computing Corporation are registered trademarks of Measurement Computing Corporation. IBM, PC, and PC/AT are trademarks of International Business Machines Corp.
1.0 SOFTWARE INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 HARDWARE INSTALLATION ..................................1 2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.2 POWER CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.3 SIGNAL CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.
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1.0 SOFTWARE INSTALLATION Before installing the board, install and run InstaCal. This package is the installation, calibration and test utility included with your board. InstaCal will guide you through switch and jumper settings for your board. Detailed information regarding these settings can be found below. Refer to the Extended Software Installation Manual for InstaCal installation instructions. 2.0 HARDWARE INSTALLATION 2.
There are two cables used with CIO-SSH16; a signal cable and a power cable. The power cable (C-PCPOWER-10) is supplied with the CIO-SSH16. The power cable is black with two white MOLEX connectors. One end mates with the J3 connector on the SSH16 and the other mates with any one of the available PC power expansion plugs inside the PC. The signal cable (C37FF-# or C37FFS-#) is a 37-conductor cable with 37D female connectors at each end.
The SSH16 requires 1 Amp of +5 volt power. You may supply this power from the PC, as we recommend, using the cable supplied, or you may use an alternate power supply. Figure 4-2. Power Connector Caution on using alternate power supplies: The analog interface from the SSH-16 to the CIO-DAS16 is a single ended voltage signal connection. As such, it is will not reject errors induced by a potential difference between the PC power supply and the alternate supply you use to power the SSH16.
connected. The nomenclature on the CIO-SSH16 corresponds to CIO-DAS16 signals. 2.4 ANALOG INPUT BOARD SETUP The analog input board must be configured for single-ended input. If the board you are using with the CIO-SSH16 supports both 8 channel differential and 16 channel single-ended configurations, set the board to 16 channels single-ended. You may also need to configure a jumper on the analog input board to supply the sample-hold signal to the CIO-SSH16.
3.0 SIGNAL CONNECTION 3.1 CONNECTOR DIAGRAM The CIO-SSH16 inputs are screw terminals which will accept 12-22 AWG wire. Each channel has a screw terminal for signal high, signal low and ground. 3.2 ANALOG INPUTS Analog inputs to the CIO-SSH16 may be connected in two different configurations. In order of complexity, these are Floating Differential and Differential. WARNING - PLEASE READ Measure the voltage between the grounds at the signal source and the PC.
A floating differential hookup is handy when the signal source is floating with respect to ground, such as a battery, 4-20 mA transmitter or thermocouple and the lead lengths are long or subject to EMI interference. The floating differential input will reject up to 10V of EMI energy on the signal wires. WARNING! Verify that the signal source is really floating. Check it with a voltmeter before risking the CIO-SSH16 and PC! 3.4 DIFFERENTIAL A differential signal is three wires from the signal source.
A laboratory instrument with its own wall plug. There are sometimes differences in wall GND between outlets.
4.0 ARCHITECTURE There are two types of functional elements on the CIO-SSH16; differential amplifiers and a sample & hold chips (LF398). Together they provide differential input and amplification for up to 16 channels of simultaneous sampling signal conditioning. This section contains information on the following subjects: y y y Amplification. Gains & signal diagram. Sample & Hold. Signal diagram, triggering, timing diagram. 4.
level signal to the analog input boards single ended inputs, reducing the impact of EMI or RFI along the signal cable between the CIO-SSH16 and the analog input board. 4.3 CIO-SSH16 vs. PROGRAMMABLE GAIN A/D BOARDS Having a dedicated differential amplifier for every channel produces flexible and powerful data acquisition capability. Data throughput of independent amplifiers exceeds that of A/D boards with single programmable gain amplifiers, even those equipped with a channel/gain queue.
Figure 4-5. Input Range Optimization During post-processing analysis, the range which provided the best resolution at any point in time is instantly available. The cost of a CIO-DAS16 and CIO-SSH16 is less than the cost of an A/D board with a channel gain queue and far less than alternative simultaneous sample & hold schemes. It certainly is more flexible. 4.
S1 S15 S16 Figure 4-6. Input Amplifiers with Sample and Hold Chips SSH OUT is synchronized to the analog input boards S&H chip and the channel select MUX. When the analog input board samples channel 0, each of the LF398s on the CIO-SSH16 also samples the signal on its input. Each of the LF398s then switches to HOLD mode and the analog input board acquires this “held” signal from each channel. The CIO-SSH16 remains in HOLD mode until the analog input board samples channel 0 again.
ANALOG INPUT BOARD’S ON-BOARD SAMPLE-HOLD CIO-SSH16 SAMPLE MODE LF398 SAMPLE/HOLD PIN 26 CIO-SSH16 SAMPLE MODE CIO-SSH16 HOLDS WHILE ANALOG IN BOARD ACQUIRES DATA Figure 4-7. Sample and Hold Timing Diagram Note that Channel 0 of the CIO-SSH16 does not have an LF398 sample and hold chip. That is because there is one sample and hold on the analog input board and it serves as the S&H chip for CIO-SSH16’s channel 0.
To calculate the effect of the droop rate on the accuracy of your measurement, the range of the signal, the resolution of the A/D converter and the time between HOLD and A/D acquisition are needed. Here is an example. RANGE CALCULATION Signal Range Gain Amplifier Output ±50 millivolts 100 ±5 Volts At full scale RESOLUTION CALCULATION A/D resolution 12 bits Volts per bit 2.44 millivolts 1 part in 4096 10/4096 TIME TO SAMPLE CALCULATION Number of channels 8 Sample Rate 4,000 samples/ sec.
5.0 SPECIFICATIONS Typical for 25°C unless otherwise specified. Power consumption +5V 1.0A typical, 1.25A max Analog input section Input amplifier type Number of channels Input range Gains INA110 16 differential ±10V X1, X10, X100, X110, X200, X210, X300, X310, X500, X510, X600, X610, X700, X710, X800, X810 Gain error Gain = 1 Gain = 10 Gain = 100 Gain = 200 Gain = 500 0.02% max, 0.002% typical 0.05% max, 0.005% typical 0.1% max, 0.01% typical 0.2% max, 0.02% typical 0.5% max, 0.
Sample / hold section Sample / hold type Aperture time Aperture uncertainty Acquisition time Temperature coefficient Droop rate RMS Noise (10 kHz to 100 kHz) LF398 250 ns max, 150 ns typical 50 ns typical 10 µs max 4 ppm/°C ±100µV/ms 10µV Current Drive Output coupling Output impedance ±5 mA DC 0.
6.0 ANALOG ELECTRONICS This short introduction to the analog electronics most often needed by data acquisition board users describes the following: y y y y y y y y y Voltage dividers. Differential vs. Single Ended Inputs. Isolation vs. Common Mode Range Low pass filters for analog and digital inputs. A/D Resolution Conversion to Engineering units. 4-20 mA inputs Noise; sources and solutions. Digital interfacing. Each deals with the impact on measurements made with data acquisition boards.
Figure 6-1. Voltage Divider The object in using a voltage divider is to choose two resistors with the proper proportions relative to the full scale of the analog or digital input and the maximum signal voltage. Dropping the voltage proportionally is often called attenuation. The formula for attenuation is: Attenuation = R1 + R2 R2 2 = 10K + 10K 10K R1 = (A-1) * R2 The variable Attenuation is the proportional difference between the signal voltage max and the full scale of the analog input.
IMPORTANT NOTE: The resistors, R1 and R2, are going to dissipate all the power in the divider circuit according to the equation Current = Voltage / Resistance. The higher the value of the resistance (R1 + R2) the less power dissipated by the divider circuit. Here is a simple rule: For Attenuation of 5:1 or less, no resistor should be less than 10K. For Attenuation of greater than 5:1, no resistor should be less than 1K. The CIO-TERMINAL has the circuitry on board to create custom voltage dividers.
A single ended input has no common mode range because there is only one LOW wire, which is assumed to be at the same level at the signal and at the A/D board. Figure 6-3. Single-Ended Input The maximum difference which may be rejected is the CMR. For example, the CIO-SSH16 has a common mode plus signal range of 11.5 volts, common mode not to exceed 10 volts. This specification is illustrated graphically here and will be referred to as Cumulative Signal Range (CSR). Figure 6-4.
the designer of the board (or other EE) would be able to translate that into a systems specification, most A/D board owners are confused or mislead by such specs. 6.3 COMMON MISUNDERSTANDINGS The CMR specification of a differential input is often confused with an isolation specification, which it is not. CMR of 10 volts is not the same as 10 volts of isolation. The graph above shows why.
associated with line voltage (60 Hz) would be filtered out but a signal of 25 Hz would be allowed to pass. Also, in a digital circuit, a low pass filter is often used to filter an input from a switch. Figure 6-5. Low pass Filter A low pass filter may be constructed from one resistor (R) and one capacitor (C). The cut off frequency is determined according to the formula: Fc = R= 1 2*Pi*R*C 1 2*Pi*C*Fc 6.6 A/D RESOLUTION & ENGINEERING UNITS Resolution is specified in bits, such as 8, 10 or 12 bits.
Resolution is a measure of the ability to differentiate between one voltage and another. Obviously, the more bits of resolution (13 bits = 8192 counts) the more divisions of full scale. The more divisions of full scale, the higher the resolution of the measurement. 6.7 ENGINEERING UNITS When a program uses an A/D board to acquire data, the data file is filled with numbers like those above.
For example, if the CIO-DAS16 board is set up to read 0 to 5 volts, then: 5 volts / 0.02 Amps = 250 Ohm shunt resistor. So a full 20 mA will register 5 volts and 4 mA will register 1 volt. To hook up the CIO-DAS16 analog inputs to a 4-20 mA transducer or signal source, place the shunt resistor across the plus and minus terminals or signal wires of the 4-20 mA. Once the resistor is in place, connect the analog input CH# Hi to the plus terminal and the analog input CH# Lo to the minus input. Figure 6-6.
specify the conditions under which the specification was made. That means the PC, the PC's power supply and the connection to the front end. Put some very good components on a circuit board and place that board in a PC and the system will be less accurate than the individual components. Some 12-bit A/D boards with the same components as a CIO-DAS16 have as little as nine bits of accuracy, due to board noise. The system specification for the CIO-SSH16 and CIO-DAS16 is +/- 1 LSB.
6.9.4 SMOOTHING DATA It is not always possible to eliminate all noise, especially with very low level sensors, but noise looks terrible when plotted and can raise doubts about otherwise excellent data. There are two simple ways to eliminate noise from the data: 1. Apply a moving average to the data if you want to retain the same apparent accuracy. 2. Remove the information from the noisy range. For example, if a 12 bit A/D converter is at +/- 5 volts (10 volts full scale) then one LSB = 10 / 4096 = 0.
For your notes.
EC Declaration of Conformity We, Measurement Computing Corp., declare under sole responsibility that the product: CIO-SSH16 Part Number Description to which this declaration relates, meets the essential requirements, is in conformity with, and CE marking has been applied according to the relevant EC Directives listed below using the relevant section of the following EC standards and other normative documents: EU EMC Directive 89/336/EEC: Essential requirements relating to electromagnetic compatibility.
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