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The GDS 8 Channel Serial Data Acquisition Pad

1 Introduction 1. 2

2 Serial communication settings 2. 2

3 Gain Ranges 3. 2

4 Channel Configuration 4. 3

5 Transducer Connections 5. 3

5.1 Acquisition Device Socket Pinout. 4

6 Software commands 6. 4

1 Introduction 1

The GDS 8 Channel Serial Data Acquisition Pad (generally referred to as the Serial Pad) is a datalogger with 8 channels of 16 bit data acquisition. Data transfer is via RS232 serial communication via a PC Comm port. Each channel can be user defined with gain range (span) settings. +/- 5 Volts supply voltage is available individually for each transducer.

2 Serial communication settings 2

Baud = 4800

Parity = n (none)

Data Bits = 8

Stop Bits = 2

3 Gain Ranges 3

The gain ranges available on the serial pad are as follows:

Gain Range 0 = +-10V

Gain Range 1 = +-5V

Gain Range 2 = +-1V

Gain Range 3 = +-200mV

Gain Range 4 = +-100mV

Gain Range 5 = +-30mV

Gain Range 6 = +-20mV

Gain Range 7 = +-10mV

The gain range can be set individually on each channel to match the transducer being used on that channel.

e.g. if a GDS 2MPa pore pressure transducer has a full scale output of 198mV at 10V excitation, an optimum gain range of +-200mV may be set giving a resolution of 200/32767 = 0.0061mV.

4 Channel Configuration 4

The 8 acquisition channels are labeled 0-7 (see figure below). Care should be taken when connecting transducers to make sure that the physical transducer connections match the transducer layout in the software. Please refer to your system/software handbook for specific channel settings.

Channel configuration for serial pad

5 Transducer Connections 5

The figure below shows the pin information for channels 0-7. The diagram is shown looking directly into the socket on the acquisition device. Transducers are connected to the pad using 5 pin DIN plugs.

5.1 Acquisition Device Socket Pinout.

Pin Number Connection

1 + 5 volts excitation

2 - 5 volts excitation

3 0 volts

4 + input from transducer

5 - input from transducer

6 Software commands 6

Any software language with use of the Comm port can be used to communicate with the serial pad. This enables users to integrate data acquisition from the serial pad into their own software. Alternatively, GDS software is available.

Commands should be transmitted via the RS232 port in ASCII, terminating with a carriage return (ASCII code 13). Data is returned in ASCII terminated with a carriage return, except for the RS command which returns a single string with fields delimited by commas and a carriage return at the end.

Command	Value	Returns	Function
Ix	x = 0 to 7	+-32767	Reads back the value from a single channel
SS		8 channels	Reads back the values from all 8 channels with carriage return
Gx,y	x = 0 - 7 y = 0 - 7	“OK”	Sets gain ranges as shown in section 2. x = channel number, y = gain range
Ax	x = 0 - 7	“OK”	Sets the number of values to average the returned value over in the form 2^x for all 8 channels
Fx,y	x = 0 - 7 y = 0 - 7	“OK”	Sets the number of values to average the returned value over for a single channel. x = channel number, y = value
SD		“OK”	Stores the setup in memory
RS			Returns all the setup values in memory For channels 0–7 returns I,G,F, followed by the Serial number and Version number

Examples:

· I5 returns the value on channel 5

· G1,3 sets the gain range on channel 1 to +-200mV

· A3 sets the average number of readings that the pad takes to return a value to 2³

· F4,2 sets the average number of readings that the pad takes to return a value on channel 4 to 2²

8 Channel Serial Pad