{"id":1377,"date":"2025-04-10T11:35:31","date_gmt":"2025-04-10T11:35:31","guid":{"rendered":"https:\/\/webprojects.cloud\/wordpress\/splatco\/?post_type=spl_knowledgebase&p=1377"},"modified":"2025-05-29T10:21:03","modified_gmt":"2025-05-29T10:21:03","slug":"hmi430-700-analog-inputs","status":"publish","type":"spl_knowledgebase","link":"https:\/\/webprojects.cloud\/wordpress\/splatco\/knowledgebase\/product-documentation\/product-documentation-controllers\/hmi430-700-product-documentation\/hmi430-700-external-inputs-and-outputs\/hmi430-700-analog-inputs\/","title":{"rendered":"HMI430\/700: Analog inputs"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

The HMI430\/700 has two analog inputs. They can each be set to measure voltage, with 0-10V range and a 0-3.3V range, 0-20mA current and temperature using an external NTC thermistor.<\/p>\n\n\n\n

Mode setting<\/h6>\n\n\n\n

The two red jumpers in the picture above set the analog input mode. The bottom one is for analog input 0, the top one is for analog input 1. Notice there are 3 positions labelled ‘V’, ‘I’ and ‘T’. The mode is determine by which pair of pins the jumper sits across.<\/p>\n\n\n\n

Jumper position<\/th>Mode<\/th><\/tr>
T<\/td>Thermistor temperature measurement mode<\/td><\/tr>
I<\/td>0-20mA<\/td><\/tr>
V<\/td>0-10V<\/td><\/tr>
No jumper<\/td>0-3.3V<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

 In the picture above analog input 0 is set for temperature, and analog input 1 is set for 0-10V.<\/p>\n\n\n\n

Connections<\/h6>\n\n\n\n

In both voltage and current modes, the pin labelled i0 or i1 must be positive with respect to the 0V pin. The picture above shows a battery connected to i1 so its voltage can be measured. Not the + polarity sign.<\/p>\n\n\n\n

For current mode this means that a typical 2-wire 4-20mA transmitter will connect between the input pin (i0 or i1) and the positive supply voltage. The full scale voltage drop (“burden voltage”) in current mode is 3.3V<\/p>\n\n\n\n

In thermistor mode and NTC thermistor simply connects between the input pin and 0V. The controller is optimised for thermistors with a resistance at 25\u00b0C of between 5K and 10K Ohm, but can be used with other resistances at reduced resolution.<\/p>\n\n\n\n

More on temperature measurement<\/h6>\n\n\n\n

Thermistor temperature measurement is a great way to go for temperatures in the range -50\u00b0C up to 120\u00b0C or more. Dollar for dollar thermistors provide the best accuracy and require very little in the way of special electronics (compared to thermocouples or RTDs). They have one drawback: they are very non-linear, so you need to do some math to get from a raw reading to an actual temperature value. Fortunately, we have made it really easy for you with the thermistor hash command<\/a>.<\/p>\n\n\n\n

The fixed excitation resistor in the HMI430 thermistor circuit is 5765\u03a9. You will generally get the best results, i.e. resolution, if you pick a thermistor with around 5K – 10K resistance at the temperature you are mainly interested in.<\/p>\n\n\n\n

Example:<\/strong> Measure in \u00b0C the thermistor connected on analog input i1. The thermistor data is:<\/p>\n\n\n\n