Use of DrDaq

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rangas2007
Newbie
Posts: 0
Joined: Sun Oct 24, 2010 7:46 am

Use of DrDaq

Post by rangas2007 »

Dear Sir,

I am using DrDaq card of Picotech for logging data from a load cell of an Instron .The voltage available from the load cell sensor is around 50-100mv depending on the load applied. I need to amplifiy this voltage in my experiment and propose to sense it with one of the external points(EXT1, EXT2 ) ports available on the DRDaq card.The DrDaq fits into the parallel port of the PC. However because we need to plug/unplug the DrDaq before and after our experimental runs we have made arrangement (to use a M!004 cable which we will get over the next week., right now we are using a local make cable) We have made the following observations in our exptl runs

a) The voltage is sensed at the Ext1 port( using a FCC64 fitted wire) without the amplifier i.e direct mV from the output point of the load cell sensor ( in this run the DrDaq card was directly fitted to the parallel port without the local make cable)

Following the breakdown of our PC we replaced the CPU and loaded the software again. This time we made sure that a local make cable was fitted into the parallel port at one end while we shall have the provision to plug/unplug the DrDaq card at the other end.We checked our installation in all aspects

b)We tried to amplify the load cell voltage with a simple inverting one ( using 741) and applied the same to the Ext1 port of DrDaq card But we failed in our expt after applying the settings, followed by starting to store fresh data. It indicated a data field of
xxxx

So we could not log the data.

c) We assumed that the EXt1 port must have got spoilt and applied the voltage to the voltage sensing pins of the Dr.Daq card. This time the settings were accepted and a constant voltage was logged ( 4-15mv) at My Voltage.(Actually we expect the voltage to increase over a 1-2 V span depending on our amplifier gain -within the limit of 5V
)


We are unable to figure out why the Ext1 port could not log our amplifier output.We need to connect the voltage from another sensor at MyVoltage port and we need to get the card to sense both the voltage ( one applied at Myvoltage and also the load cell output at Ext1 port) simultaneously eventually.

a)Can you suggest any particular opamp that we need to used for interfacing with the DrDaq card and load cell output ?
b)Is our problem related to the connecting of a local make cable between the port of the Pc and the DrDaq card.

c)Will our problem get solved by the M1004 cable?


Kindly reply on urgent basis,


Thanking you,

Yours faithfully,

B.Sobha
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ziko
Advanced User
Advanced User
Posts: 1705
Joined: Fri Dec 01, 2006 10:03 am
Location: St Neots

Re: Use of DrDaq

Post by ziko »

Hi,

Have you used a sense resistor?

External Inputs
Each external input socket has four connections:

Pin 1 Input channel with 100k pull-up to 2.5 V
Pin 2 Ground
Pin 3 Sensor type detect with 100k pull-up to 2.5 V
Pin 4 Power approx 2mA at 3-5V

Kind regards
Ziko

Technical Specialist

rangas2007
Newbie
Posts: 0
Joined: Sun Oct 24, 2010 7:46 am

Re: Use of DrDaq--urgent

Post by rangas2007 »

scaling---->use scaling from file------>displays---> C:// ....//picofull/Ext1 custom voltage . On clicking OK we get the message " The scaling method was not valid .---> not accepted as win32application.

What more function calls must be incorporated for the file to be recognised.
We tried again adding the following function on the top of the above mentioned software file.
PREF1 short PREF2 drdaq_open_unit (
short port);

But the data fileld logged is 'xxxxxx'' volts.


KIndly help out on urgent basis.



Thanking you,

B.Sobha
-->
Dear Sir,

Yes , I have placed a sense resistor of 3.3 K ohm and have incorporated the following .dds file into the picolog executable directory-C://program files/pIco/Picofull'....as suggested by Mr Peter French.We connected only a single voltage of 2V to be sensed at the external ports. The connections to the FCC68 cable are

Pin1--Signal input---2V , Pin2 and 3 --3.3K ohms sense resistor , pin 4 --left unconnected on advice from Mr Peter

[Scale1]
Resistor=3.3
LongName=Custom Voltage 1
Units=Volts
MinValue=0
MaxValue=5.0
OutOfRange=0
Places=3
Method=0
NoOfPoints=2
Raw1=0
Scaled1=0
Raw2=2.5
Scaled2=5.0

When going about doing the New settings we had the problem under parameter options-->scaling---->use scaling from file------>displays---> C:// ....//picofull/Ext1 custom voltage . On clicking OK we get the message " The scaling method was not valid .---> not accepted as win32application.

What more function calls must be incorporated for the file to be recognised.
We tried again adding the following function on the top of the above mentioned software file.
PREF1 short PREF2 drdaq_open_unit (
short port);

But the data fileld logged is 'xxxxxx'' volts.


KIndly help out on urgent basis.



Thanking you,

B.Sobha