CA 37

Thermocouple conditioners

General

CA-37 are isolated single channel signal conditioners that amplify, compensate, filter, isolate and convert voltage signals from thermocouples to a level suitable for connection to a data acquisition system, Industrial PC, PLC, or other measuring system. The conditioners work with thermocouples J, K, T, E, R, S, B and N.

Isolated modules protect people and measuring equipment and galvanically separate it from excessive events that may occur on the sensor side or elsewhere within the measurement environment. The module input is protected from voltage levels and transients up to 250 Vrms. The isolation voltage is 1,500 V.

The CA-37 signal conditioner family can be mixed with other isolated module families within the same application. They can be plugged into and off the measuring system without switching off the power supply voltage or interrupting the system (hot swapable).

The thermocouple signal is processed through a preamplifier and then the signal is filtered and transmitted through the transformer isolation barrier by amplitude modulation technique which gives high linearity, stability and good characteristics. After isolation, the signal is reconstructed with a fourth-order filter and converted to a standard current or voltage output level.

Prices and models of CA-37

Characterisation

The CA-37 works with eight types of thermocouples: J, K, T, E, R, S, B, and N, which are most commonly encountered in industrial applications. It has built-in compensation for the cold junction of the thermocouple (CJC), which compensates for the error caused by the voltage generated due to the temperature at the cold junction of the thermocouple (conditioner connections). A thermocouple break detection circuit is installed as well as a lower scale that the user can complete by adding an external resistor of 47 MOm to terminals 2 and 4.

On the front of the module, under the clear cover, are two multi-turn trimmers for precise offset and zero adjustment. Both ​​are factory-set and the user can recalibrate them if needed.

The central component of the module is the signal isolation transformer. Like most transformers, this one has a primary and a secondary side. Using this terminology, the input side of the module is "primary side" and the output side of the module is called "secondary side". A sensor is connected to the primary side of the module and the secondary side of the module is connected to a data acquisition and measurement system, an analog input module of an Industrial PC or PLC, to a panel meter or other measuring system.

Transformer signal isolation uses an amplitude modulation method to obtain linear, stable and reliable characteristics. This technique produces better results than digital or linear optocouplers or capacitor isolation techniques. The primary side of the module is galvanically isolated or "floating" relative to the secondary side of the module and relative to the power supply. The signal demodulator on the secondary side of the module restores the original signal, which is then filtered and buffered to achieve low noise and low output impedance.

CA-37 Series Isolation Modules have a built-in fifth order filter, of which the first Anti-aliasing pole is located in the primary circuit of the module while a fourth order filter is located on the secondary side of the isolation barrier. After Anti-aliasing filtering, the signal is brought to the chopper stage behind which is a specially designed micro transformer. In the secondary stage, behind the insulation barrier, the signal is demodulated and re-filtered from transmission spikes and interference. The output of the module can be a voltage or current signal as needed.

The warranty period is 7 years and the service period is 10 years. It comes with a user guide in English and a calibration list.

CA-37 with 110/220V AC power supply (option)

The base version of the CA-37 works with a standard DC power supply of 19 to 30V DC (24V DC nominal). However, if the application requires the power supply of a 220V AC coder, which is not a rare case, then the user can order a conditioner with the suffix A. This type of conditioner works with an AC voltage of 85 to 265V or with a DC voltage of 100 to 400V. These two power supplies make the CA-36 applicable in many situations. Some users use these conditioners in an environment that is powered by a 110V battery, or in elevated AC voltage conditions in transformer stations.

On this conditioner model, there are three terminals for connecting the power supply: L, N and GND (Picture on the left). The L should connect the phase, neutral to N, and  GND to the ground. Grounding, apart from the safety function, has the function of reducing the internal voltage unit oscillations, so it should be connected in any case. If the DC power supply is used, it must be connected to the L and N connectors (the order is not relevant).

Relay (option)

The isolation conditioner family CA-37 with the suffix R has a built-in relay with a working and quiet contact on the external terminals. The relay can switch on or off to 240V, 6A, and can be set to activate when the input size is greater than the specified value or when the input size is less than the set value. There is a working and quiet contact on the copies. The relay has a built-in hysteresis control that can be fine tuned with a precision multi-port trimmer potentiometer.

The only limitation for this version is that if it is used with 220V power supply (version with suffix A), the relay has only a working contact.

The setting of the relay activation level is performed by the potentiometer on the front of the conditioner. In order to avoid the oscillation of the relay when the input size is the same, the hysteresis is assigned to the device. Hysteresis in the first case, when the relay is activated and when the input is higher than the set value, indicates the size for how much the input size should be smaller than the specified size for activating the relay to turn it off. In the second case, it indicates how much the input size should be to be higher than the set to switch off the relay. Hysteresis can be set to 1% or 5% span with an internal jumper.

If the load is applied to the relay of the inductive character, it is necessary to add the "snubber" from the outside in parallel to the relay contacts. The values ​​of the supply components are calculated, but can also be determined empirically for the given application. Generally, even if the load is applied to the relay of the inductive type, a capacitor of 0.2 uF per line with a 10 Ohm resistor can be used. For optimum performance, the supply wheel must be calculated because this is the best way to optimally extinguish the spark at the relay.