A-D converters:   DataTakers

Note for all A-D converters:   Modern Macs lack built-in serial ports, so you'll need a USB to serial converter and driver software.    The units made by Keyspan (now, TrippLite), specifically the USA-19HS, function reliably with LabHelper.   Other brands have not worked well, or at all.
Other A-D converters:

Data Electronics DataTakers  are expensive, rugged, and highly capable (although not particularly fast).    Several models are available; all use the same (or very similar) basic instruction set and all are impressively versatile.   They have only 5-12 numbered hardware inputs, but several different instrument outputs can be connected simultaneously   to each input, greatly increasing the number of sensors that can be monitored.     An analog input on a DataTaker 800, 80, or 85-series has 4 connectors labeled    #, +, - , and *.    On a DataTaker 500 and related models, R is used instead of #.

  • For differential voltage readings, connect your leads to the + and - terminals.

  • For other voltage inputs (including thermocouples) connect the ground or neutral lead to # (or R)   and the other lead to +, -, or *.   When using thermocouples, be sure to indicate the thermocouple type in the DataTaker inputs window.

  • Resistance measurements require two-wire connections to either the + and -   or the * and # (or R) terminals.
You must use the DataTaker inputs option in the External A-D device   submenu in the A-D menu to specify which connectors are in use, and for what purpose (volts, resistance, or thermocouples); this option is called automatically whenever you're using a DataTaker and add a new channel.     You can also use the channel as a high-speed counter, but this involves a different set of inputs.    Thus, one DataTaker hardware input can be used for several logical channels.  

  • DataTakers come with screw terminals (DT50/500/600/80/85) or 'cage clamp' (DT800) terminals to which you can directly attach instrument recorder cables.  However, you may want to build your own junction box with connectors that are easier to use -- especially if you change instrument inputs frequently. 

  • DataTakers have the digital output channels necessary to control external devices, such as gas multiplexers.  However, they use open collector outputs that may not produce enough positive voltage to act as a digital 'high' value.   Adding this simple circuit will solve the problem.   It can be powered by the onboard voltage source on DataTakers:   +5V on a DT500 series or +12V on a DT800.

    • •    DT50, 500, 600 series   The DT50 has 5 channels of high-resolution analog-to-digital conversion; the others in this series have 10 A-D channels; the 600 series have an LCD display and simple keypad but are otherwise the same as the DT500 (note that early DT500s had a black case as shown in the picture below; this was changed in later models to a rather garish purple, as seen in the picture of a DT600 at left).

                 As described above, each A-D channel can be set up to read voltages, resistances, or thermocouples, or can be used as a digital counter.   Four digital I/O lines are available (for controlling external devices).
               These DataTakers can communicate at speeds of up to 9600 baud (4800 is recommended), and are limited to sampling rates of no more than about 5/sec for most applications.

      Note:   I have not tested all of the many versions of the DT50/500/600 series with LabHelper, but they should function similarly.   I have used the DT500 fairly extensively and users report no problems with the DT50.

    The cable joining these DataTakers to the computer (more specifically, to the USB --> serial converter) needs to have the correct connections.   The wiring diagram in the DataTaker manual for IBM-compatible 9-pin (DB9) connectors works well.

    Note:      Because of their low sampling and communication rates, these DataTakers cannot be used in oscilloscope mode.   

    •    DT800 series   The DataTaker 800 series are more modern, higher-speed versions of this sophisticated A-D converter.   The basic DT800 has 12 channels of high-resolution analog-to-digital conversion; each channel can be set up to read voltages, resistances, or thermocouples, or can be used as a digital counter.   Eight digital output lines are available (for controlling external devices).
               DataTaker 800s communicate at a default rate of 57.6 Kbaud and can handle 115.2 Kbaud, and hence can gather data faster than other DataTaker models.  However, they're still fairly slow compared to the Sable UI2.   The DT800's conversion speed varies with the type of data (e.g., thermocouple or resistance readings take longer than simple voltage readings), but you can expect about 20 samples/sec on single channels in 'high accuracy' mode and 50 samples/sec in 'high speed' mode; additionally, there is a 'burst' mode that can take intermittent readings at sample rates of several kilohertz (go here and here for details).

    The cable joining the DT800 to the USB --> serial converter needs to have the correct connections.   The wiring diagram in the DataTaker 800 manual for IBM-compatible 9-pin (DB9) connectors works well.   In brief, it requires two female DB9 connectors and 5 conductors:

         •    join pins 5 on both DB9s

         •    join pin 3 on one DB9 to pin 2 on the other, and vice versa

         •    join pin 7 on one DB9 to pin 8 on the other, and vice versa

    Since the communication speed is fairly high, do not make the cable longer than a couple of meters.

    Note:    The DataTaker 800 can be used in oscilloscope mode, but maximum sampling rates are fairly low.    The main constraint is the speed of the serial connection.    Using the DT800 in oscilloscope mode is described in more detail here.

    The following DataTaker models share control language with the DT800 and should work with LabHelper, but I have not tested them.

    •   If anyone tries to use them, I'd appreciate hearing about how successful the attempt was.

    •    DT80 and 85 series   The DT80 and DT85 are medium-speed DataTakers (up to about 25 samples/second) that differ in the number of analog inputs:    5 on the DT80 and 16 on the DT85.   There have been several within-model upgrades over the years, and there are multiple versions of each (with and without cell phone modems, etc.).
                The DT80 and DT85 series have the same versatile A-D connectors as the other DataTakers, with up to three sensors connected to each input -- so the DT80 can read up to 15 instruments or sensors, and the DT85 can handle up to 48.   Both have several channels of digital output that can be used to control external devices.
                These DataTakers can communicate at speeds of up to 115,200 baud (57,600 is the default), which should be sufficient to prevent the serial transfer rate from limiting maximum sampling speed (as happens to some extend with the DT800).

    The cable joining the DT80 or DT85 to the USB --> serial converter needs to have the correct connections, but these are simple: only three conductors are needed (as shown clearly in the operator's manual).

    Note:    The DataTaker 80 and 85 can be used in oscilloscope mode, but maximum sampling rates are pretty low.

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