This is differential pressure transmitter response video. This video demonstrate the different of pressure transmitter response on low and high ports. The pressure transmitter is connected with the battery circuit and the voltmeter is connected in parallel to two hundred fifty ohm resistor. The pressure transmitter has two ports they are high pressure port and low pressure port. First, this video show the function of the high pressure ports by applying the positive pressure on the high pressure port. When the positive pressure is applied, the voltage will increase. Here is the tutorial video:

Then apply the positive pressure on the low pressure port. When the positive pressure is applied on the low pressure port, the voltage will decrease. This video also demonstrate the effect of using negative pressure on the high pressure port and the low pressure port. When the negative pressure is applied on the high pressure port, the  voltage is decreased, like positive pressure on the low pressure port. And,  When the negative pressure is applied on the low pressure port, the  voltage is increase, like positive pressure on the high pressure port.