PicoLog 1000
Small Terminal Board
User’s Guide
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Pico Technology Small Terminal Board User Guide
CONTENTS
1 Overview 1
1.1 Introduction 1
1.2 Specifications 1
1.3 Connecting the Terminal Board to the Data Logger 1
1.4 Terminals and solder pads 2
2 Making measurements 2
2.1 Measuring voltages up to +2.5 V 2
2.2 Measuring voltages above +2.5 V 3
2.3 Offsetting and scaling the sensor signal 4
2.4 Resistor Connections 5
2.5 Measuring current 7
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Small Terminal Board User Guide Pico Technology
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Pico Technology Small Terminal Board User Guide
1 Overview
1.1 Introduction
The Small Terminal Board (PP545) is an accessory for the PicoLog 1012 and 1216
Data Loggers. The screw terminals allow sensor wires to be attached to the data
logger without soldering. The terminal board also has locations where you can fit
resistors to extend the input ranges of the logger.
Figure 1 - Small Terminal B oard
1.2 Specifications
Dimensions 66 x 72 x 17 mm (approx. 2.6 x 2.83 x 0.67 in.)
Weight 50 g nominal (approx. 1.76 oz)
Terminal wire size 0.6-1.6 mm (14-22 AWG)
1.3 Connecting the Terminal Board to the Data Logger
You can plug the Terminal Board directly into the analog connector on the PicoLog
Data Logger, or you can use a standard 25-way male-D to female-D parallel cable
to connect the two units.
Using a cable will increase the noise and crosstalk between channels. If you make
your own cable, you can minimise this problem by using a signal/ground twisted
pair for each channel.
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1.4 Terminals and solder pads
The table below shows the purpose of each of the screw terminals and resistor
locations on the Terminal Board. For details of the inputs and outputs of the data
logger, see the PicoLog 1012 and 1216 User’s Guide.
Marking on
Description
Terminal
Board
C1…C16 * Analog input channels 1 to 16 *
D0…D3 Digital outputs
GND Circuit ground
2.5 2.5 volt power output for sensors
PWM Pulse-width modulated output
R1, R3, R5 etc. Locations for 0805 or leaded series resistors in analog inputs (see
Figure 5). Before you fit a resistor in one of these sites, you must
cut the track under the component (see Figure 6).
R2, R4, R6 etc. Solder pads for 0805 or leaded shunt resistors between each
analog input and GND (see Figure 5).
* The PicoLog 1216 has channels 1 to 16.
The PicoLog 1012 has channels 1 to 12.
Table 1 - Terminals and resistor sites
2 Making measurements
2.1 Measuring voltages up to +2.5 V
For voltage sources from 0 V to +2.5 V, you can connect directly to any analog
input channel. With this method, there is no need to fit any additional components
to the Terminal Board.
Figure 2 shows analog channel 1, but the connections are similar for the other
channels.
Small Terminal Board
C1
V
IN
(0 V to
+2.5 V)
GND
Figure 2 - Direct input to channel
PicoLog Data Logger
Channel 1
R
ADC
V
1 MΩ
ADC
GND
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Pico Technology Small Terminal Board User Guide
2.2 Measuring voltages above +2.5 V
For voltages above +2.5 V, use a voltage divider connection. You must cut one
track on the Terminal Board and fit two 0805 surface-mount, or axial leaded,
resistors for each channel that you wish to use in this way.
Figure 3 shows the voltage divider circuit for analog channel 1, but the connections
are similar for the other channels.
Small Terminal Board
C1
V
IN
Channel 1
GND
R
1
R
2
PicoLog Data Logger
Channel 1
R
ADC
1 MΩ
V
ADC
GND
Figure 3 - Voltage divider
The voltage that the ADC sees, V
, depends on VIN and the values of R1 and R2,
ADC
and is given by the following equation:
RV
2IN
V
ADC
Choose values of R
RR
21
and R2 so that V
1
is approximately +2.5 V when VIN is at its
ADC
highest.
To minimise errors in the measured voltage, V
voltage V
, ensure that the combined resistance of R1 + R2 is much greater than
IN
, caused by loading of the source
ADC
the resistance of the voltage source. If you are unsure of the resistance of the
voltage source, use large values for R
If you have chosen a value for R
and R2 such that R1 + R2 is about 10 kΩ.
1
that is greater than 10 kΩ and you need high
2
accuracy, then you will need to take into account the ADC’s input resistance R
which is in parallel with R
parallel equivalent resistance of R
. Use the following formula to obtain a value for the
2
and R
2
ADC
, RP:
ADC
,
RR
ADC2
R
P
RR
ADC2
where R
= 1 MΩ, and then use RP instead of R2 in the previous formula.
ADC
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Small Terminal Board User Guide Pico Technology
2.3 Offsetting and scaling the sensor signal
Example using a 2.5 V input
It is possible to offset and scale the ±5.0 V signal from your sensor. There is a
+2.5 V, 10 mA source available on the PicoLog Data Logger.
Assuming you are using channel 1, add a 20 kΩ surface mount or leaded resistor in
position R1 (cutting the link as in Figure 6). Add a second 20 kΩ surface mount or
leaded resistor in position R2. Finally, to give the correct offset and final scaling you
must add a 10 kΩ leaded resistor in position R33. These three resistors will scale
the ±5 V output of your sensor to a signal at the logger varying from 0 V to +2.5 V.
The scaling function of PicoLog can convert this reduced and offset range back to
the original voltage reading by mathematically subtracting 1.25 V and multiplying
the remainder by 4. To compensate for any residual errors, the actual scaling offset
and multiplier can be slightly varied to give exact readings by doing a simple
calibration, if required.
If required, all 16 channels can be offset in this way. The above values allow use up
to the full analogue bandwidth of the PicoLog of 70 kHz but the input impedance is
reduced from 1 MΩ to about 27 kΩ.
If a higher input impedance is required, replace R1 with 1 MΩ, do not fit R2 at all
and for the R33 use 500 kΩ (two 1 MΩ in parallel). This will give an input
impedance of over 1 MΩ but the frequency response will fall to about 1 kHz.
In both cases, when no input is connected, the DC voltage will float up to 1.66 V.
As long as the output impedance of the sensor you are feeding to the input of the
PicoLog is much lower than input impedance of the circuit above, the DC level is
pulled to the correct value upon connection.
Small Terminal Board
R
33
(10 k)
R
1
PicoLog Data Logger
+2.5 V
(20 k)
C1
(±5.0 V)
GND
R
V
IN
R
2
(20 k)
ADC
1 MΩ
Channel 1
V
ADC
0 to 2.5 V
GND
Figure 4 – Offsetting and scaling the signal
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Pico Technology Small Terminal Board User Guide
2.4 Resistor connections
The resistors on the Small Terminal Board are connected as shown in Figure 5.
R26
R58R62
R59
R27
IN_CH14 OUT_CH14
R14
R46
R47
R15
IN_CH8 OUT_CH8
R34
R2
R66
R3
R67
2.5V
R33
R57
R25
IN_CH13 OUT_CH13
R13
R45
IN_CH7 OUT_CH7
R1
R65
R28
R60
R16
R48
R4
R68
R35
R29
R61
IN_CH15 OUT_CH15
R17
R49
IN_CH9 OUT_CH9
R5
R37
R30
R18
R50
R6
R38
R36
R63
R31
IN_CH16 OUT_CH16
R19
R51
IN_CH10 OUT_CH10
R7
R39
R32
R64
R20
R52
R22
R54
R21
R53
IN_CH11 OUT_CH11
R8
R40
R10
R42
R9
R41
R23
R55
IN_CH12 OUT_CH12
R43
R11
R24
R56
R12
R44
IN_CH1 OUT_CH1
IN_CH2 OUT_CH2
IN_CH3 OUT_CH3
IN_CH4 OUT_CH4
IN_CH5 OUT_CH5
IN_CH6 OUT_CH6
Figure 5 - Voltage divider resistor sites
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Small Terminal Board User Guide Pico Technology
The location for each series resistor (R1 and so on) is bypassed by a copper link.
You must cut this link (see Figure 6) before fitting the resistor.
Cut this link
before fitting
R1
Figure 6 - Location of copper link under R1
The following noise problems are often associated with potential divider circuits:
1. Noise from source voltage Try fitting a capacitor as described
2. RF interference picked up at
high-impedance points
3. Noise on the earth connections The signal 0 V line is connected to
Should either 1 or 2 above occur and you want to try a capacitor, ensure that you
have fitted resistor R
capacitor in place of or in parallel with R
for C, the value of the capacitor:
C
where R is R
hertz.
or the smaller of R1 and R
1
and cut the corresponding track beneath the resistor. Fit the
1
1
Rf2
π
below.
Smaller values for R1 and R2 may help
mains earth. Try to avoid this
situation.
, as necessary. Use the following formula
2
, and f is the highest signal frequency in
2
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Pico Technology Small Terminal Board User Guide
2.5 Measuring current
You can use measure current towards ground by using a simple shunt resistor to
convert the current into a voltage before measuring with the ADC.
Figure 7 shows the circuit for analog channel 1, with shunt resistor R
. A similar
2
circuit can be used for the other channels.
Small Terminal Board
I
IN
C1
V
IN
GND
R
2
PicoLog Data Logger
Channel 1
R
ADC
V
1 MΩ
ADC
GND
Figure 7 - Shunt resistor circuit
You will need to calculate the resistor value R
V 2.5
I
MAX
where I
R
2
is the highest current you want to measure.
MAX
from the following equation:
2
Warning!
Under no circumstances use this method for measuring mains (house)
currents. The Small Terminal Board is not designed to be connected t o the
mains. Attempting to do so could result in serious property damage and
personal injury.
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Issues:
1) 14.5.09. New for PicoLog 1012 & 1216.
2) 11.2.11. New SMT design.
3) 04.1.13. Title changed
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United Kingdom
www.picotech.com
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8 DO161-3
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