Gain
Max V
Min V
Unipolar
1
5.07
-0.01
Unipolar
2
2.53
-0.01
Unipolar
4
1.26
-0.01
Unipolar
8
0.62
-0.01
Bipolar
1
5.07
-5.18
Table 2.7.2-1. Nominal Analog Input Voltage Ranges
The high-resolution converter on the UE9-Pro only supports the 0-5 and +/-5 volt ranges.
The readings returned by the analog inputs are raw binary values (low level functions). An approximate voltage conversion can be
performed as:
Volts(uncalibrated) = (Bits/65536)*Span
Where span is the maximum voltage minus the minimum voltage from the table above. For a proper voltage conversion, though,
use the calibration values (Slope and Offset) stored in the internal flash on the Control processor.
Volts = (Slope * Bits) + Offset
In both cases, “Bits” is always aligned to 16-bits, so if the raw binary value is 24-bit data it must be divided by 256 before
converting to voltage. Binary readings are always unsigned integers.
Since the UE9 uses multiplexers, all channels (except 129-135 and 137-143) have the same calibration for a given input range.
See Section 5.6 for details about the location of the UE9 calibration constants
2.7.3 - Typical Analog Input Connections
A common question is “can this sensor/signal be measured with the UE9”. Unless the signal has a voltage (referred to UE9
ground) beyond the limits in Appendix A, it can be connected without damaging the UE9, but more thought is required to
determine what is necessary to make useful measurements with the UE9 or any measurement device.
Voltage (versus ground): The analog inputs on the UE9 measure a voltage with respect to UE9 ground. When measuring
parameters other than voltage, or voltages too big or too small for the UE9, some sort of sensor or transducer is required to
produce the proper voltage signal. Examples are a temperature sensor, amplifier, resistive voltage divider, or perhaps a
combination of such things.
Impedance: When connecting the UE9, or any measuring device, to a signal source, it must be considered what impact the
measuring device will have on the signal. The main consideration is whether the currents going into or out of the UE9 analog input
will cause noticeable voltage errors due to the impedance of the source. See Appendix A for the recommended maximum source
impedance.
Resolution (and Accuracy): Based on the selected input range and resolution of the UE9, the resolution can be determined in
terms of voltage or engineering units. For example, assume some temperature sensor provides a 0-10 mV signal, corresponding
to 0-100 degrees C. Samples are then acquired with the UE9 using the 0-5 volt input range and 16-bit resolution, resulting in a
voltage resolution of about 5/65536 = 76 µV. That means there will be about 131 discrete steps across the 10 mV span of the
signal, and the overall resolution is 0.76 degrees C. If this experiment required a resolution of 0.1 degrees C, this configuration
would not be sufficient. Accuracy will also need to be considered. Appendix A places some boundaries on expected accuracy, but
an in-system calibration can generally be done to provide absolute accuracy down to the INL limits of the UE9.
Speed: How fast does the signal need to be sampled? For instance, if the signal is a waveform, what information is needed: peak,
average, RMS, shape, frequency, … ? Answers to these questions will help decide how many points are needed per waveform
cycle, and thus what sampling rate is required. In the case of multiple channels, the scan rate is also considered. See Sections 3.1
and 3.2.
2.7.3.1 - Signal from the LabJack
Each analog input on the UE9 measures the difference in voltage between that input and ground (GND). Since all I/O on the UE9
share a common ground, the voltage on a digital output or analog output can be measured by simply connecting a single wire from
that terminal to an AINx terminal.
2.7.3.2 - Unpowered Isolated Signal
An example of an unpowered isolated signal would be a thermocouple or photocell where the sensor leads are not shorted to any
external voltages. Such a sensor typically has two leads. The positive lead connects to an AINx terminal and the negative lead
connects to a GND terminal.
An exception might be a thermocouple housed in a metal probe where the negative lead of the thermocouple is shorted to the
metal probe housing. If this probe is put in contact with something (engine block, pipe, …) that is connected to ground or some
other external voltage, care needs to be taken to insure valid measurements and prevent damage.
2.7.3.3 - Signal Powered by the LabJack
A typical example of this type of signal is a 3-wire temperature sensor. The sensor has a power and ground wire that connect to Vs
and GND on the LabJack, and then has a signal wire that simply connects to an AINx terminal.
10
Summary of Contents for UE9
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