pico Technology USB DrDAQ User Manual Download Page 29

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USB DrDAQ User's Guide

usbdrdaq.en r4

The Signal Input channel has 100 kΩ pull-up resistors to 2.5 V, so that the input can
be either a resistance or a voltage.

Here is a block diagram of a typical USB DrDAQ sensor:

1 = Signal input
2 = Ground
3 = Auto Detect
4 = Power

2.10.2 Powering the sensor

A definition of a sensor is:

A device giving a signal for the detection or measurement of a physical property to
which it responds.

The sensor's properties must be known before work can begin on designing some way
of interfacing it to the USB DrDAQ (sensor scaling).

There are two types of sensor:

Active Sensors

These require power (excitation) from an external source to

generate an output signal. Examples of active sensors include:

Property

Sensor

Output

Temperature

Silicon

Voltage / Current

RTD

Resistance

Thermistor

Resistance

Force / Pressure

Strain Gauge

Resistance

Acceleration

Accelerometer

Capacitance

Humidity

Capacitor

Resistance

Light

LDR

Resistance

Position

LVDT

AC Voltage

Passive Sensors

These do not require any power to generate an output. Typical

examples are:

Property

Sensor

Output

Temperature

Thermocouple

Voltage

Force/pressure

Piezoelectric

Voltage

Position

Variable resistor

Resistance

Light Intensity

Photodiode

Current

Summary of Contents for USB DrDAQ

Page 2: ......

Page 3: ...cope timebase 8 4 Using the trigger 8 5 Adding spectrum views 9 6 Adjusting the RGB LED 10 7 Controlling the digital outputs 11 7 Specifications and connections 11 1 General specifications 11 2 Input output and sensor specifications 12 3 Connections 13 8 Channel scaling 13 9 External sensors 13 1 Overview 13 2 DD100 Temperature Sensor 14 3 DD011 pH Electrode 16 4 PP066 Reed Switch 17 5 DD101 Humid...

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Page 5: ...BNC or exposed metalwork of USB DrDAQ to anything which may be at some voltage other than ground as doing so may cause damage to the unit If in doubt use a meter to check that there is no significant AC or DC voltage For computers that do not have an earth connection for example laptops it must be assumed that USB DrDAQ is not protected by an earth in the same way a battery multimeter is not prote...

Page 6: ...ment or software is suitable for a given application It is your responsibility therefore to ensure that the product is suitable for your application Mission critical applications This software is intended for use on a computer that may be running other software products For this reason one of the conditions of the licence is that it excludes usage in mission critical applications for example life ...

Page 7: ...s Sockets for external sensors Use USB DrDAQ to capture fast signals for example sound waveforms Digital output for control experiments Simply plug in to your PC and measure supplied with both PicoScope oscilloscope and PicoLog data logging software 2 2 Overview The USB DrDAQ features 16 channels comprising sensors inputs and outputs These are covered in more detail in Specifications These connect...

Page 8: ... use even for newcomers to oscilloscopes and data loggers Once you have followed the simple steps listed below you will soon be on your way to becoming an expert 1 Install the software Load the CD ROM that is included with your scope device then click the Install Software link and follow the on screen instructions 2 Plug in the USB DrDAQ device Windows will recognise it and prepare your computer t...

Page 9: ...waveform The green Start button will be highlighted to show that PicoScope is ready Adjacent to this is the red Stop button 3 Try clicking your fingers over the microphone and the trace on the screen should react USB DrDAQ is now successfully installed and working A typical finger click trace Problems Help is at hand Our technical support staff are always ready to answer your telephone call during...

Page 10: ...n Add a channel by clicking on the sensor you d like to activate In this example we have activated the Light sensor once activated the trace will appear and the Light button will be highlighted in blue You can add other channels to the oscilloscope screen by simply clicking on the sensor that you wish to view In this example we have added Temp While the trace is running put your finger on the temp...

Page 11: ...013 Pico Technology Ltd All rights reserved usbdrdaq en r4 2 6 3 Changing the oscilloscope timebase The timebase can be adjusted by selecting the drop down menu shown below Change the timebase to 50 ms div to change the display as follows ...

Page 12: ...or press the space bar and select a single trigger using the trigger options at the bottom of the screen Press the space bar to start PicoScope and click your fingers over the microphone The single trigger option means that PicoScope stops running when it has captured a signal 2 6 5 Adding spectrum views So far we have looked at the oscilloscope functions PicoScope allows USB DrDAQ to be used as a...

Page 13: ...e USB DrDAQ units include an RGB LED The colour of this LED can be changed by clicking the LED icon above the oscilloscope window The following drop down will appear Clicking Enable LED Control will show the numerical values for the LED to glow RED The colour of the LED is adjusted by dragging the individual colour and brightness sliders entering specific RGB values or clicking within the colour d...

Page 14: ...ections click the digital output icon above the oscilloscope window The following drop down will appear Moving any of the 4 sliders to High will activate that digital output Only outputs 1 and 2 are able to output a PWM Pulse Width Modulation signal To do this click the Digital Out icon above the oscilloscope window and choose PWM in the drop down for either digital output 1 or 2 This allows adjus...

Page 15: ...evel Input 55 to 100 dBA 1 dBA 5 dBA Temperature Input 10 to 70 C 0 1 C 25 C 2 C 25 C Light Input 0 to 100 0 1 Not calibrated RGB LED Output 16 7 million colour 8 bit x 3 N A pH sensor Redox ORP Input 0 to 14 pH 2 V 1012Ω 0 02 pH 1 2 mV Sensor calibration dependent Resistance Input 0 to 1 MΩ 250 Ω 10 kΩ 5 Scope voltage Input 1 25 V 2 5 V 5 V 10 V with 100 kHz bandwidth 8 bit 3 Digital 1 I O 2 2 kΩ...

Page 16: ...ion outside of its range can cause degradation to other signals being recorded To view the specifications for each channel refer to Input output and sensor specifications External Inputs Each external input socket has four connections Pin Function 1 Input channel with 100k pull up to 2 5 V 2 Ground 3 Sensor type detect with 100k pull up to 2 5 V 4 Power up to 100 mA 5V not protected limited Refer ...

Page 17: ...well as the built in sensors USB DrDAQ has sockets for optional external sensors When a sensor is plugged in to the external sensor sockets the software detects it and automatically scales readings For example if a temperature sensor is plugged in readings are displayed in C or if a humidity sensor is plugged in readings are displayed in RH External sensors are optional extras and can be purchased...

Page 18: ...or with most pH meters and data loggers To minimize these errors a temperature sensor can be connected to Ext 1 and the DrDAQ will compensate for temperature changes Testing pH Electrodes The best way to test a pH electrode is to use pH buffers pH 4 pH 7 and pH 10 buffers are widely available If you do not have any pH buffers then distilled deionized water will have a pH near 7 some still mineral ...

Page 19: ... the procedure for each of the buffer solutions Don t forget to wash the probe between buffers 4 You should now have a table of readings similar to the one below pH Buffer value at 25 C Measured value from USB DrDAQ 4 01 4 06 7 00 7 07 10 01 9 92 pH calibration with PicoLog As already mentioned you will need to note down the measured pH value and compare it with the actual value to create a lookup...

Page 20: ...y use the unit to connect a simple single pole switch such as a micro switch to USB DrDAQ You will need to obtain a switch and some insulated connecting wire Remember to keep magnets or magnetic fields away from the unit when you use it with an external switch Magnetic fields will still make the internal reed switch operate overriding the open setting of the external switch To connect the switch f...

Page 21: ...accuracy Reading 10 Operating temperature 0 60 C Resolution 0 2 Relative Humidity Minimum response time 60 seconds with vigorous air movement Maximum response time 60 minutes in still air Caution Do not allow the DD101 sensor to become wet The DD101 is a non condensing sensor and liquid including condensation inside the case may damage it The DD101 may be connected to either Ext 1 Ext 2 or Ext 3 o...

Page 22: ...Pico DD100 Temperature Sensor At least two Standard Solutions A label for the DD101 A test container An insulated box A stand for the DD101 Optional high accuracy calibrated reference laboratory standard humidity gauge Stand It is very important that the standard solution does not enter the case of the DD101 The solution may damage the electrical components of the sensor Therefore the DD101 needs ...

Page 23: ...itrate 54 Magnesium chloride 33 Note The humidity produced by the standard solution depends on the temperature If the temperature changes from 20 to 21 Celsius this could give a change in relative humidity of as much as 3 for a nominal 50 value This change would be worse for higher values of relative humidity Insulated box Because the humidity produced by the standard solution depends on temperatu...

Page 24: ...de the test container for at least one hour You must wait for the temperature to stabilize and the DD101 to provide correct readings This may take up to eight hours if you have used a large container 9 Check that the USB DrDAQ plots for temperature and humidity have been constant over the last few minutes of your measurements If you are using a calibrated reference take a reading now Take care to ...

Page 25: ...r it into the Pico software to calibrate the sensor 1 Open the PicoLog Parameter Scaling Dialog 2 Start PicoLog Recorder 3 Click on Settings 4 Click on Input Channels The DrDAQ Measurements dialog appears 5 Select the input channel for the humidity sensor for example External 1 Humidity 6 Click on the Edit button The Edit DrDAQ Measurements dialog appears 7 Click on the Options button The Paramete...

Page 26: ...e sensor with the label Testing Sensors You can check whether a sensor is working properly or not by running through the calibration procedure If you find that the sensor values differ from the standard values by more than 10 you may have a damaged sensor In this case contact Pico for assistance 2 9 6 DD103 Oxygen Sensor The DD103 Oxygen Sensor is used to measure the percentage of oxygen in a gas ...

Page 27: ...e then this reading is currently displayed on the PicoLog monitor view Complete the table above with this value and follow the instructions below 1 Select the Settings Input channels menu item and click OK 2 Select the Oxygen sensor from the list then click Edit 3 Click on Options then Scaling 4 From the drop down Scaling method menu select Table lookup 5 From the look up table you completed above...

Page 28: ...ogue input that represents the sensor reading There are four pins on the External inputs This view is looking into the Ext socket on USB DrDAQ in the direction of entry of the plug Pin 1 Signal Input Pin 2 Ground Pin 3 Auto Detect Pin 4 Supply Voltage Suitable connectors to these external inputs are FCC 68 4 4 plugs Alternatively the USB DrDAQ sensor adapter break out box from Lascells can be used...

Page 29: ...designing some way of interfacing it to the USB DrDAQ sensor scaling There are two types of sensor Active Sensors These require power excitation from an external source to generate an output signal Examples of active sensors include Property Sensor Output Temperature Silicon Voltage Current RTD Resistance Thermistor Resistance Force Pressure Strain Gauge Resistance Acceleration Accelerometer Capac...

Page 30: ...on the sensor which can compensate for any manufacturing irregularities Sensor Scaling Hardware With both these types of sensors it is essential that the USB DrDAQ displays an accurate representation of the property to be measured There are many factors to take into account when designing scaling circuitry Sensitivity The USB DrDAQ has 12 bit resolution over the 0 to 2 5 V input range This means t...

Page 31: ...may give a different output value when rising to a voltage than when falling to a voltage This is difficult to eliminate and should be taken into account Once the sensor has been selected and all of the above has been considered the design of some scaling circuitry can begin There are many ICs on the market that can be purchased cheaply that deal with the above potential problems Look into these b...

Page 32: ...is would give using Ohm s Law 0 4 volts at 4 mA 2 4 volts at 20 mA P VxI Therefore 50 mW resistor required Example 3 Measuring 10 volts Notes This is a simple circuit that uses a potential divider to reduce the voltage going into the USB DrDAQ by a factor of four R1 3k R2 1k The resistors are calculated using Ohm s Law V IR Auto Detect Auto detect resistor is placed between Ground Pin 2 and Signal...

Page 33: ...enu choose Digital Output Set Chann to Digital Output 2 and High Choose OK Click Apply and choose OK Start the trace and place the tip of a finger onto the temperature sensor on the USB DrDAQ The trace should rise and upon overlapping the mask the LED connected to digital connection 2 should illuminate PicoLog The following is a short example of how to activate an LED via a digital output on the U...

Page 34: ...the Scale section heading A set of typical entries from a DDS file is shown below Scale1 Resistor 1 LongName CustomTemperature1 ShortName TempC Units C MinValue 40 MaxValue 120 OutOfRange 0 Places 1 Method 0 IsFast Yes NoOfPoints 32 Raw1 2 385 Scaled1 30 Raw32 1 32 Scaled32 100 Scale2 Resistor 2 2 LongName CustomTemperature2 ShortName TempF Units F MinValue 32 MaxValue 160 Scale3 Resistor 3 3 Long...

Page 35: ...te For PicoScope these values will determine the maximum and minimum values displayed in Oscilloscope View For PicoLog these values determine what Maximum range is displayed in the Graph View set in the Graph Options dialog Places 1 Number of decimal places The options are 0 1 2 and 3 With places 1 the value 15 743 would be returned as 157 meaning 15 7 With places 2 the same value would be returne...

Page 36: ...However all input channels of a USB DrDAQ are calibrated during manufacture Calibration involves measuring a known value such as the temperature of boiling water or the resistance of a known resistor or the values shown by a calibrated sensor then converting these values into the units you need Linear Single Point Calibration When calibrating a sensor with a linear response curve it may only be ne...

Page 37: ...tween the operating range and the full input range of the sensor since it would be far more difficult to calibrate the sensor between 200 C and 200 C and would yield no accuracy benefit for the user between 5 C and 110 C Non Linear Multi point Calibration You will need more than two points to describe a non linear response curve and therefore you will need to create a look up table experimentally ...

Page 38: ...ut menu The latest versions of PicoScope can check for updates automatically and will advise you if an update is available The latest version of all our software can be downloaded free of charge from the Pico Technology web site at http www picotech com Alternatively the latest software can also be purchased on CD To be kept up to date with news of new software releases join our e mail mailing lis...

Page 39: ...uired number of samples If as is usually the case the signal contains a small amount of noise this technique can increase the effective vertical resolution of the oscilloscope PC Oscilloscope A virtual instrument formed by connecting a PicoScope oscilloscope to a computer running the PicoScope software PicoScope software A software product that accompanies all PicoScope oscilloscopes It turns your...

Page 41: ...face 17 L Laptops 1 3 LED 9 10 29 Legal information 2 M Making your own sensors 24 Measuring pH 14 O Overvoltage protection 11 Oxygen sensor 22 P pH electrode 14 PicoLog How to use 4 PicoScope How to use 5 Powering a sensor 25 PP066 Reed Switch 16 R Reed switch 16 Repair 1 3 Resolution 11 RGB 9 10 29 S Safety warning 1 3 Sampling rate 11 Scaling 13 26 Scaling files 30 Sensors adding 13 Software In...

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Page 44: ...mes House Colmworth Business Park ST NEOTS Cambridgeshire PE19 8YP United Kingdom Tel 44 0 1480 396 395 Fax 44 0 1480 396 296 www drdaq com Copyright 2013 Pico Technology Ltd All rights reserved usbdrdaq en r4 17 05 2013 ...

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