Kipp & Zonen CT24 User manual

0305 260
SIGNAL AMPLIFIER 4 - 20 mA
INSTRUCTION MANUAL

IMPORTANT USER INFORMATION
1
IMPORTANT USER INFORMATION
Reading this entire manual is recommended for full
understanding of the use of this product
Should you have any comments on the product or this manual we
will be pleased to receive them at:
Kipp & Zonen B.V.
Röntgenweg 1 2624 BD Delft Holland
P.O. Box 507 2600 AM Delft Holland
Phone [phone]
Fax [phone]
E-mail [email protected]
Kipp & Zonen reserve the right to make changes in the
specifications without prior notice.
WARRANTY AND LAIBILITY
Kipp & Zonen guarantees that the product delivered has
been thoroughly tested to ensure that it meets its
published specifications. The warranty included in the
conditions of delivery is valid only if the product has been
installed and used according to the instructions supplied
by Kipp & Zonen.
Kipp & Zonen shall in no event be liable for incidental or
consequential damages, including without limitation, lost
profits, loss of income, loss of use and other related
exposures, however caused, arising from the faulty and
incorrect use of the product.

IMPORTANT USER INFORMATION
2
COPYRIGHT©2004 KIPP & ZONEN
All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system or transmitted in
any form or by any means, without permission in written
form from the company.
Manual version: 0604

IMPORTANT USER INFORMATION
3
Declaration of Conformity
According to EC guideline 89/336/EEC 73/23/EEC
We Kipp & Zonen B.V.
Röntgenweg 1
2624 BD Delft
Declare under our sole responsibility that the product
Type: CT 24
Name: Solar Sensor Amplifier 4 – 20 mA
To which this declaration relates is in conformity with the
following standards:
Imissions EN 50082-1 Group standard
IEC 1000-4-2
IEC 1000-4-3
IEC 1000-4-4
Emissions EN 50081-1 Group standard
EN 55022
Safety standard IEC 1010-1
Following the provisions of the directive
B.A.H. Dieterink
President
KIPP & ZONEN B.V.

IMPORTANT USER INFORMATION
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TABLE OF CONTENTS
5
TABLE OF CONTENTS
IMPORTANT USER INFORMATION...............................1
Declaration of Conformity .............................................3
TABLE OF CONTENTS...................................................5
1. GENERAL INFORMATION ...................................7
2. SPECIFICATIONS .................................................9
3. CONNECTION OF THE CT 24 ............................11
3.1 Minimising interference ........................................13
3.2 Selecting the supply voltage ................................14
3.3 Connection for current output...............................15
3.4 Connection for voltage output ..............................17
4. NEGATIVE INPUT SIGNALS ..............................21
5. CALIBRATION PROCEDURE ............................23
5.1 Standard calibration .............................................23
5.2 Special calibration. ...............................................25
6. PART NUMBERS ................................................27

TABLE OF CONTENTS
6

GENERAL INFORMATION
7
1. GENERAL INFORMATION
With the CT 24 it is possible to convert a low level voltage
output from a solar sensor to the standard level of 4 – 20
mA or (using the installed 500 Ohm resistor) to a 2 – 10
Volt signal.
The CT 24 amplifier is designed to use with Kipp & Zonen
solar sensors, to allow long cables between sensor and
data logger without external interference.
The large operation temperature range from - 30°C to +
70°C and the waterproof housing (IP 65) makes that the
CT 24 can be used under the same conditions as all solar
sensors.
The amplification can be adjusted from the standard 0 –
20 mV is 4 – 20 mA to a value that takes the calibration
factor of the sensor into account, like 0 – 1600 W/m² is 4
– 20 mA.
Even negative inputs are allowed through a positive shift
of the zero point from +4 to + 8 mA. This allows for
negative input signals of about 250 W/m² like a
pyrgeometer and net radiometer produces.
The CT 24 is protected against reversed polarity, voltage
surges on input and output lines and is shielded against
EMF disturbance.
For pyranometers with temperature sensors there are
special connector strips in the CT 24 to connect these
sensors from in going to out-going cable.

GENERAL INFORMATION
8

SPECIFICATIONS
9
2. SPECIFICATIONS
Current output range nominal 4 to 20 mA
Voltage output range @ R L = 500 Ω2 to 10 V
Gain, factory set 1 mA / mV +/- 0.1%
Gain adjust +0.5 to +1.0 mA / mV
Zero, factory set +4 mA +/- 0.1%
Zero adjust +3 to +8 mA
Non-linearity < 0.1%
Temperature dependence of gain within +/- 0.01% / K
Zero drift typical +/- 0.4 µV / K
Input impedance 1 MΩ
Input range @ gain 0.5, zero 4 mA 0 to +32 mV
@ gain 0.5, zero 8 mA -8 to +24 mV
@ gain 1, zero 4 mA 0 to +16 mV
@ gain 1, zero 8 mA -4 to +12 mV
Power supply @ R L ≤100 Ωmin. 12 to 30 VDC
Power supply for voltage output 10V min. 20 VDC
Temperature range (operating) -30°C to +70°C
Housing Aluminium, grey lacquered
Dimensions W x D x H 64 x 58 x 34 mm
Water proof IP 65 / DIN 40050
Cable glands size 4 to 6,5 mm

SPECIFICATIONS
10

CONNECTION OF THE CT24
11
3. CONNECTION OF THE CT 24
The CT 24 is meant to boost the (low level) output signal
of a solar sensor. Therefore the CT 24 amplifier needs to
be close to the sensor to maintain a high signal to noise
ratio in the cable.
The internal layout of the CT 24 is shown in figure 3.1.
figure 3.1 Internal layout of the CT 24
To prevent errors due to current loops
between input and output it is necessary
that the sensor outputs are floating (not
connected to ground) or that the (−) from
the power supply is not connected to
ground.

CONNECTION OF THE CT24
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The passive Kipp & Zonen sensors have floating outputs
(not connected to sensor housing or shield), so the inputs
of the CT 24 will be floating.
Actually the rule of thumb is that any connection
between CT 24 input LO and output LO is not allowed
(e.g. accidentally both grounded).
In case of doubt check the impedance of the sensor wires
against the sensor housing, this should be infinite.

CONNECTION OF THE CT24
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3.1 Minimising interference
Use sensors with shielded cables.
All Kipp & Zonen sensor cables have an internal shield
that can be connected to a ground.
Many passive Kipp & Zonen sensors have the shield
connected to the sensor housing. If the sensor is
mounted to a grounded frame, the shield of the input
cable is grounded too.
If the grounding at the sensor is not sure, but shielding is
necessary, the shield can be grounded via the output
cable or at the CT 24. For this purpose pin 1 of the input
connector strips can be used or one of the screws that
holds the PC board in place.
The output cable can be unshielded or shielded.
SHIELD 1 1 SHIELD
SIGNAL −INPUT 2 2 SIGNAL −OUTPUT
SIGNAL + INPUT 3 3 SIGNAL + OUTPUT
INTERCONNECTION 4 4 INTERCONNECTION
INTERCONNECTION 5 5 INTERCONNECTION
INTERCONNECTION 6 6 INTERCONNECTION
INTERCONNECTION 7 7 INTERCONNECTION
INTERCONNECTION 8 8 INTERCONNECTION
INTERCONNECTION 9 9 INTERCONNECTION
figure 3.2 internal connection strip

CONNECTION OF THE CT24
14
3.2 Selecting the supply voltage
The CT 24 operates as a so-called 2 wire current
transmitter. This means that the amplifier receives its
operating current from the loop that represents the
current output signal.
The loop has to be powered with a power supply or active
receiver capable of providing a voltage between 12 and
30 Volt @ 100 Ohm “loop resistance”. When later on the
current is to be transformed to a voltage, it is important to
select the power supply voltage in accordance with the
desired output voltage.
Example: Required voltage over the CT 24 is 10 Volt
(minimum value)
Required voltage over the 500 Ohm resistor
is 10 Volt (@ 20mA)
This implies that the supplied voltage has to
be at least 10+10 = 20 Volt.
Be aware that an active sensor (with some electronics)
can generally not be powered together with its CT 24 by
the same power supply. In that case the sensor output is
normally connected with the common of the power supply
and consequently also with the CT 24 output LO. This is
against the rule of thumb.

CONNECTION OF THE CT24
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3.3 Connection for current output
When the CT 24 is used as a standard 4−20 mA amplifier
(transmitter) only 2 input and 2 output wires have to be
connected plus two times the shielding of both cables.
This configuration is least sensitive to shielding and
grounding problems, because the voltage variations in
the cable leads are relative small.
Grounding and coupling of the shields from input cable
and output cable is often no problem and the power
supply and data logger common may be grounded as
well, preferably all at the same ground.
The cable coming from the sensor is lead through the
cable gland and directly connected to pin 2 (-) and 3 (+)
of the input connector strip.
Check your sensor manual for the colour of the wires.
The outgoing cable has the same number of wires as the
input cable and can be connected to the output strip.
Make sure both cables have their shield connected to
ground.
Input connector pins number 4 till 9 are interconnected
with the output connector pins and can be used to
transfer the signal from temperature sensors like a Pt100
or thermistor to the output cable.
(First remove the 500 Ωresistor from the terminal strip).

CONNECTION OF THE CT24
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figure 5.3 connection for current output
Shield
Power supply +
Current out

CONNECTION OF THE CT24
17
3.4 Connection for voltage output
When a voltage signal is needed directly from the CT 24,
the conversion from current to voltage can be made
inside the CT 24. For this purpose a precision 500 Ohm
resistor is supplied that can be connected through the
connection strip. This requires however four wires. The
wires used to supply the current and the wires that carry
the voltage output can not be combined. Even though the
return from the current loop and the low of the voltage
output are connected to the same level, the voltage drop
over the cable makes it necessary to use separate wires
for the voltage output.
figure 3.4 voltage output connection
Power supply +
Signal +
Signal –
Power supply –
Shield

CONNECTION OF THE CT24
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So when the CT 24 is used with a voltage output, 2 input
and 4 output wires have to be connected plus two times
the shielding of both cables.
Of course any other RLcan be used to transform the
output current to a voltage, as long as the guideline from
chapter 5 is followed. (E.g. RL= 50 Ωto make an output
voltage range of 0.2 to 1 V ).
If the resistor is placed at the end of the current loop
(near the power supply), only two wires are necessary.
The power supply but also the loop
“indicator” or passive receiver should be
floating from ground to give highest freedom
of connection or configuration.
With a voltage output connection it is most advantageous
to use a power supply and read out equipment both
floating from ground.
Only in that case the shield of the input cable or the
sensor housing (and not more) can be grounded at the
sensor side.
Connect only input cable shield and output cable shield
together, if you have to ground at the data logger side.
The CT 24 will oscillate probably, but connecting the
signal+ of the data logger to the same ground will stop
this. This is of course only possible with floating data
logger and floating power supply of course.
(At principle a shielded output cable is no must and the
input cable shield can also be carried on to the data
logger by a single wire).

CONNECTION OF THE CT24
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At this place we have to precise the rule of thumb. The
oscillating occur due to a certain capacitive coupling (>
500 pF) between CT 24 input LO and common of power
supply and data logger, especially in the voltage output
mode with the internal RL= 500 Ωactive. The capacitive
loop consists of a capacitance from input leads to
(grounded) input cable shield. This capacitance is in
series with the capacitances from power supply- and data
logger- and the corresponding lead in the cable to
respectively ground and output cable shield.
The effect of the coupling can be minimized by using a
very short input cable, an unshielded output cable and/or
making the output voltage swing as low as possible,
preferable by using the current output configuration or by
reducing the voltage swing to 0.2 to 1 V with an
RL = 50 Ω.
Consequently if power supply – and/or data logger – are
connected to a ground, grounding the shield of the input
cable directly or via the sensor housing introduces
oscillation of the CT 24.
Generally speaking no second ground reference is
tolerated in a configuration with power supply or data
logger connected to ground.
Consequently no shielding against external E.M. fields is
possible and also the sensor housing must be floating.
The application field of this configuration is therefore
restricted and should be tested at location firstly.